diff --git a/backend/alembic/versions/026_add_user_role_and_system_config.py b/backend/alembic/versions/026_add_user_role_and_system_config.py
new file mode 100644
index 0000000..9bb863a
--- /dev/null
+++ b/backend/alembic/versions/026_add_user_role_and_system_config.py
@@ -0,0 +1,101 @@
+"""Add role, mfa_enforce_pending, must_change_password to users; create system_config table.
+
+Revision ID: 026
+Revises: 025
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "026"
+down_revision = "025"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # 1. Add role column with server_default for existing rows
+    op.add_column("users", sa.Column(
+        "role", sa.String(30), nullable=False, server_default="standard"
+    ))
+
+    # 2. Add MFA enforcement pending flag
+    op.add_column("users", sa.Column(
+        "mfa_enforce_pending", sa.Boolean(), nullable=False, server_default="false"
+    ))
+
+    # 3. Add forced password change flag (SEC-12)
+    op.add_column("users", sa.Column(
+        "must_change_password", sa.Boolean(), nullable=False, server_default="false"
+    ))
+
+    # 4. Add last_password_change_at audit column
+    op.add_column("users", sa.Column(
+        "last_password_change_at", sa.DateTime(), nullable=True
+    ))
+
+    # 5. Add CHECK constraint on role values (SEC-16)
+    op.create_check_constraint(
+        "ck_users_role",
+        "users",
+        "role IN ('admin', 'standard', 'public_event_manager')"
+    )
+
+    # 6. Promote the first (existing) user to admin
+    op.execute(
+        "UPDATE users SET role = 'admin' WHERE id = (SELECT MIN(id) FROM users)"
+    )
+
+    # 7. Create system_config table (singleton pattern -- always id=1)
+    op.create_table(
+        "system_config",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("allow_registration", sa.Boolean(), nullable=False, server_default="false"),
+        sa.Column("enforce_mfa_new_users", sa.Boolean(), nullable=False, server_default="false"),
+        sa.Column("created_at", sa.DateTime(), nullable=False, server_default=sa.text("NOW()")),
+        sa.Column("updated_at", sa.DateTime(), nullable=False, server_default=sa.text("NOW()")),
+        sa.PrimaryKeyConstraint("id"),
+        # SEC-09: Enforce singleton row
+        sa.CheckConstraint("id = 1", name="ck_system_config_singleton"),
+    )
+
+    # 8. Seed the singleton row
+    op.execute(
+        "INSERT INTO system_config (id, allow_registration, enforce_mfa_new_users) "
+        "VALUES (1, false, false)"
+    )
+
+    # 9. Create audit_log table
+    op.create_table(
+        "audit_log",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("actor_user_id", sa.Integer(), nullable=True),
+        sa.Column("target_user_id", sa.Integer(), nullable=True),
+        sa.Column("action", sa.String(100), nullable=False),
+        sa.Column("detail", sa.Text(), nullable=True),
+        sa.Column("ip_address", sa.String(45), nullable=True),
+        sa.Column("created_at", sa.DateTime(), nullable=False, server_default=sa.text("NOW()")),
+        sa.PrimaryKeyConstraint("id"),
+        sa.ForeignKeyConstraint(["actor_user_id"], ["users.id"]),
+        sa.ForeignKeyConstraint(
+            ["target_user_id"], ["users.id"], ondelete="SET NULL"
+        ),
+    )
+    op.create_index("ix_audit_log_actor_user_id", "audit_log", ["actor_user_id"])
+    op.create_index("ix_audit_log_target_user_id", "audit_log", ["target_user_id"])
+    op.create_index("ix_audit_log_action", "audit_log", ["action"])
+    op.create_index("ix_audit_log_created_at", "audit_log", ["created_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_audit_log_created_at", table_name="audit_log")
+    op.drop_index("ix_audit_log_action", table_name="audit_log")
+    op.drop_index("ix_audit_log_target_user_id", table_name="audit_log")
+    op.drop_index("ix_audit_log_actor_user_id", table_name="audit_log")
+    op.drop_table("audit_log")
+    op.drop_table("system_config")
+    op.drop_constraint("ck_users_role", "users", type_="check")
+    op.drop_column("users", "last_password_change_at")
+    op.drop_column("users", "must_change_password")
+    op.drop_column("users", "mfa_enforce_pending")
+    op.drop_column("users", "role")
diff --git a/backend/alembic/versions/027_add_user_id_to_todos.py b/backend/alembic/versions/027_add_user_id_to_todos.py
new file mode 100644
index 0000000..4a60855
--- /dev/null
+++ b/backend/alembic/versions/027_add_user_id_to_todos.py
@@ -0,0 +1,38 @@
+"""Add user_id FK to todos table.
+
+Revision ID: 027
+Revises: 026
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "027"
+down_revision = "026"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("todos", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE todos SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_todos_user_id", "todos", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("todos", "user_id", nullable=False)
+    op.create_index("ix_todos_user_id", "todos", ["user_id"])
+    op.create_index("ix_todos_user_completed", "todos", ["user_id", "completed"])
+    op.create_index("ix_todos_user_due_date", "todos", ["user_id", "due_date"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_todos_user_due_date", table_name="todos")
+    op.drop_index("ix_todos_user_completed", table_name="todos")
+    op.drop_index("ix_todos_user_id", table_name="todos")
+    op.drop_constraint("fk_todos_user_id", "todos", type_="foreignkey")
+    op.drop_column("todos", "user_id")
diff --git a/backend/alembic/versions/028_add_user_id_to_reminders.py b/backend/alembic/versions/028_add_user_id_to_reminders.py
new file mode 100644
index 0000000..75a2dbb
--- /dev/null
+++ b/backend/alembic/versions/028_add_user_id_to_reminders.py
@@ -0,0 +1,36 @@
+"""Add user_id FK to reminders table.
+
+Revision ID: 028
+Revises: 027
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "028"
+down_revision = "027"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("reminders", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE reminders SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_reminders_user_id", "reminders", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("reminders", "user_id", nullable=False)
+    op.create_index("ix_reminders_user_id", "reminders", ["user_id"])
+    op.create_index("ix_reminders_user_remind_at", "reminders", ["user_id", "remind_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_reminders_user_remind_at", table_name="reminders")
+    op.drop_index("ix_reminders_user_id", table_name="reminders")
+    op.drop_constraint("fk_reminders_user_id", "reminders", type_="foreignkey")
+    op.drop_column("reminders", "user_id")
diff --git a/backend/alembic/versions/029_add_user_id_to_projects.py b/backend/alembic/versions/029_add_user_id_to_projects.py
new file mode 100644
index 0000000..f5f9031
--- /dev/null
+++ b/backend/alembic/versions/029_add_user_id_to_projects.py
@@ -0,0 +1,36 @@
+"""Add user_id FK to projects table.
+
+Revision ID: 029
+Revises: 028
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "029"
+down_revision = "028"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("projects", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE projects SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_projects_user_id", "projects", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("projects", "user_id", nullable=False)
+    op.create_index("ix_projects_user_id", "projects", ["user_id"])
+    op.create_index("ix_projects_user_status", "projects", ["user_id", "status"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_projects_user_status", table_name="projects")
+    op.drop_index("ix_projects_user_id", table_name="projects")
+    op.drop_constraint("fk_projects_user_id", "projects", type_="foreignkey")
+    op.drop_column("projects", "user_id")
diff --git a/backend/alembic/versions/030_add_user_id_to_calendars.py b/backend/alembic/versions/030_add_user_id_to_calendars.py
new file mode 100644
index 0000000..ef1b621
--- /dev/null
+++ b/backend/alembic/versions/030_add_user_id_to_calendars.py
@@ -0,0 +1,36 @@
+"""Add user_id FK to calendars table.
+
+Revision ID: 030
+Revises: 029
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "030"
+down_revision = "029"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("calendars", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE calendars SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_calendars_user_id", "calendars", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("calendars", "user_id", nullable=False)
+    op.create_index("ix_calendars_user_id", "calendars", ["user_id"])
+    op.create_index("ix_calendars_user_default", "calendars", ["user_id", "is_default"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_calendars_user_default", table_name="calendars")
+    op.drop_index("ix_calendars_user_id", table_name="calendars")
+    op.drop_constraint("fk_calendars_user_id", "calendars", type_="foreignkey")
+    op.drop_column("calendars", "user_id")
diff --git a/backend/alembic/versions/031_add_user_id_to_people.py b/backend/alembic/versions/031_add_user_id_to_people.py
new file mode 100644
index 0000000..60ee2bc
--- /dev/null
+++ b/backend/alembic/versions/031_add_user_id_to_people.py
@@ -0,0 +1,36 @@
+"""Add user_id FK to people table.
+
+Revision ID: 031
+Revises: 030
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "031"
+down_revision = "030"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("people", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE people SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_people_user_id", "people", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("people", "user_id", nullable=False)
+    op.create_index("ix_people_user_id", "people", ["user_id"])
+    op.create_index("ix_people_user_name", "people", ["user_id", "name"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_people_user_name", table_name="people")
+    op.drop_index("ix_people_user_id", table_name="people")
+    op.drop_constraint("fk_people_user_id", "people", type_="foreignkey")
+    op.drop_column("people", "user_id")
diff --git a/backend/alembic/versions/032_add_user_id_to_locations.py b/backend/alembic/versions/032_add_user_id_to_locations.py
new file mode 100644
index 0000000..996a207
--- /dev/null
+++ b/backend/alembic/versions/032_add_user_id_to_locations.py
@@ -0,0 +1,34 @@
+"""Add user_id FK to locations table.
+
+Revision ID: 032
+Revises: 031
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "032"
+down_revision = "031"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("locations", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE locations SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_locations_user_id", "locations", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("locations", "user_id", nullable=False)
+    op.create_index("ix_locations_user_id", "locations", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_locations_user_id", table_name="locations")
+    op.drop_constraint("fk_locations_user_id", "locations", type_="foreignkey")
+    op.drop_column("locations", "user_id")
diff --git a/backend/alembic/versions/033_add_user_id_to_event_templates.py b/backend/alembic/versions/033_add_user_id_to_event_templates.py
new file mode 100644
index 0000000..5ca90a4
--- /dev/null
+++ b/backend/alembic/versions/033_add_user_id_to_event_templates.py
@@ -0,0 +1,34 @@
+"""Add user_id FK to event_templates table.
+
+Revision ID: 033
+Revises: 032
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "033"
+down_revision = "032"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("event_templates", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE event_templates SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_event_templates_user_id", "event_templates", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("event_templates", "user_id", nullable=False)
+    op.create_index("ix_event_templates_user_id", "event_templates", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_event_templates_user_id", table_name="event_templates")
+    op.drop_constraint("fk_event_templates_user_id", "event_templates", type_="foreignkey")
+    op.drop_column("event_templates", "user_id")
diff --git a/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py b/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py
new file mode 100644
index 0000000..81b3a3d
--- /dev/null
+++ b/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py
@@ -0,0 +1,46 @@
+"""Add user_id FK to ntfy_sent table, rebuild unique constraint as composite.
+
+Revision ID: 034
+Revises: 033
+Create Date: 2026-02-26
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "034"
+down_revision = "033"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("ntfy_sent", sa.Column("user_id", sa.Integer(), nullable=True))
+    op.execute(
+        "UPDATE ntfy_sent SET user_id = ("
+        "  SELECT id FROM users WHERE role = 'admin' ORDER BY id LIMIT 1"
+        ")"
+    )
+    op.create_foreign_key(
+        "fk_ntfy_sent_user_id", "ntfy_sent", "users",
+        ["user_id"], ["id"], ondelete="CASCADE"
+    )
+    op.alter_column("ntfy_sent", "user_id", nullable=False)
+
+    # Drop old unique constraint on notification_key alone
+    op.drop_constraint("ntfy_sent_notification_key_key", "ntfy_sent", type_="unique")
+
+    # Create composite unique constraint (per-user dedup)
+    op.create_unique_constraint(
+        "uq_ntfy_sent_user_key", "ntfy_sent", ["user_id", "notification_key"]
+    )
+    op.create_index("ix_ntfy_sent_user_id", "ntfy_sent", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_ntfy_sent_user_id", table_name="ntfy_sent")
+    op.drop_constraint("uq_ntfy_sent_user_key", "ntfy_sent", type_="unique")
+    op.create_unique_constraint(
+        "ntfy_sent_notification_key_key", "ntfy_sent", ["notification_key"]
+    )
+    op.drop_constraint("fk_ntfy_sent_user_id", "ntfy_sent", type_="foreignkey")
+    op.drop_column("ntfy_sent", "user_id")
diff --git a/backend/app/jobs/notifications.py b/backend/app/jobs/notifications.py
index cd3099e..bcd0961 100644
--- a/backend/app/jobs/notifications.py
+++ b/backend/app/jobs/notifications.py
@@ -19,6 +19,7 @@ from app.database import AsyncSessionLocal
 from app.models.settings import Settings
 from app.models.reminder import Reminder
 from app.models.calendar_event import CalendarEvent
+from app.models.calendar import Calendar
 from app.models.todo import Todo
 from app.models.project import Project
 from app.models.ntfy_sent import NtfySent
@@ -55,10 +56,11 @@ async def _mark_sent(db: AsyncSession, key: str) -> None:
 
 async def _dispatch_reminders(db: AsyncSession, settings: Settings, now: datetime) -> None:
     """Send notifications for reminders that are currently due and not dismissed/snoozed."""
-    # Mirror the filter from /api/reminders/due
+    # Mirror the filter from /api/reminders/due, scoped to this user
     result = await db.execute(
         select(Reminder).where(
             and_(
+                Reminder.user_id == settings.user_id,
                 Reminder.remind_at <= now,
                 Reminder.is_dismissed == False,  # noqa: E712
                 Reminder.is_active == True,  # noqa: E712
@@ -72,8 +74,8 @@ async def _dispatch_reminders(db: AsyncSession, settings: Settings, now: datetim
         if reminder.snoozed_until and reminder.snoozed_until > now:
             continue  # respect snooze
 
-        # Key ties notification to the specific day to handle re-fires after midnight
-        key = f"reminder:{reminder.id}:{reminder.remind_at.date()}"
+        # Key includes user_id to prevent cross-user dedup collisions
+        key = f"reminder:{settings.user_id}:{reminder.id}:{reminder.remind_at.date()}"
         if await _already_sent(db, key):
             continue
 
@@ -98,9 +100,13 @@ async def _dispatch_events(db: AsyncSession, settings: Settings, now: datetime)
     # Window: events starting between now and (now + lead_minutes)
     window_end = now + timedelta(minutes=lead_minutes)
 
+    # Scope events through calendar ownership
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == settings.user_id)
+
     result = await db.execute(
         select(CalendarEvent).where(
             and_(
+                CalendarEvent.calendar_id.in_(user_calendar_ids),
                 CalendarEvent.start_datetime >= now,
                 CalendarEvent.start_datetime <= window_end,
                 # Exclude recurring parent templates — they duplicate the child instance rows.
@@ -116,8 +122,8 @@ async def _dispatch_events(db: AsyncSession, settings: Settings, now: datetime)
     today = now.date()
 
     for event in events:
-        # Key includes the minute-precision start to avoid re-firing during the window
-        key = f"event:{event.id}:{event.start_datetime.strftime('%Y-%m-%dT%H:%M')}"
+        # Key includes user_id to prevent cross-user dedup collisions
+        key = f"event:{settings.user_id}:{event.id}:{event.start_datetime.strftime('%Y-%m-%dT%H:%M')}"
         if await _already_sent(db, key):
             continue
 
@@ -141,13 +147,13 @@ async def _dispatch_events(db: AsyncSession, settings: Settings, now: datetime)
 
 async def _dispatch_todos(db: AsyncSession, settings: Settings, today) -> None:
     """Send notifications for incomplete todos due within the configured lead days."""
-    from datetime import date as date_type
     lead_days = settings.ntfy_todo_lead_days
     cutoff = today + timedelta(days=lead_days)
 
     result = await db.execute(
         select(Todo).where(
             and_(
+                Todo.user_id == settings.user_id,
                 Todo.completed == False,  # noqa: E712
                 Todo.due_date != None,  # noqa: E711
                 Todo.due_date <= cutoff,
@@ -157,7 +163,8 @@ async def _dispatch_todos(db: AsyncSession, settings: Settings, today) -> None:
     todos = result.scalars().all()
 
     for todo in todos:
-        key = f"todo:{todo.id}:{today}"
+        # Key includes user_id to prevent cross-user dedup collisions
+        key = f"todo:{settings.user_id}:{todo.id}:{today}"
         if await _already_sent(db, key):
             continue
 
@@ -185,6 +192,7 @@ async def _dispatch_projects(db: AsyncSession, settings: Settings, today) -> Non
     result = await db.execute(
         select(Project).where(
             and_(
+                Project.user_id == settings.user_id,
                 Project.due_date != None,  # noqa: E711
                 Project.due_date <= cutoff,
                 Project.status != "completed",
@@ -194,7 +202,8 @@ async def _dispatch_projects(db: AsyncSession, settings: Settings, today) -> Non
     projects = result.scalars().all()
 
     for project in projects:
-        key = f"project:{project.id}:{today}"
+        # Key includes user_id to prevent cross-user dedup collisions
+        key = f"project:{settings.user_id}:{project.id}:{today}"
         if await _already_sent(db, key):
             continue
 
@@ -213,6 +222,18 @@ async def _dispatch_projects(db: AsyncSession, settings: Settings, today) -> Non
             await _mark_sent(db, key)
 
 
+async def _dispatch_for_user(db: AsyncSession, settings: Settings, now: datetime) -> None:
+    """Run all notification dispatches for a single user's settings."""
+    if settings.ntfy_reminders_enabled:
+        await _dispatch_reminders(db, settings, now)
+    if settings.ntfy_events_enabled:
+        await _dispatch_events(db, settings, now)
+    if settings.ntfy_todos_enabled:
+        await _dispatch_todos(db, settings, now.date())
+    if settings.ntfy_projects_enabled:
+        await _dispatch_projects(db, settings, now.date())
+
+
 async def _purge_old_sent_records(db: AsyncSession) -> None:
     """Remove ntfy_sent entries older than 7 days to keep the table lean."""
     # See DATETIME NOTE at top of file re: naive datetime usage
@@ -240,29 +261,35 @@ async def run_notification_dispatch() -> None:
     """
     Main dispatch function called by APScheduler every 60 seconds.
     Uses AsyncSessionLocal directly — not the get_db() request-scoped dependency.
+
+    Iterates over ALL users with ntfy enabled. Per-user errors are caught and
+    logged individually so one user's failure does not prevent others from
+    receiving notifications.
     """
     try:
         async with AsyncSessionLocal() as db:
-            result = await db.execute(select(Settings))
-            settings = result.scalar_one_or_none()
+            # Fetch all Settings rows that have ntfy enabled
+            result = await db.execute(
+                select(Settings).where(Settings.ntfy_enabled == True)  # noqa: E712
+            )
+            all_settings = result.scalars().all()
 
-            if not settings or not settings.ntfy_enabled:
+            if not all_settings:
                 return
 
             # See DATETIME NOTE at top of file re: naive datetime usage
             now = datetime.now()
-            today = now.date()
 
-            if settings.ntfy_reminders_enabled:
-                await _dispatch_reminders(db, settings, now)
-            if settings.ntfy_events_enabled:
-                await _dispatch_events(db, settings, now)
-            if settings.ntfy_todos_enabled:
-                await _dispatch_todos(db, settings, today)
-            if settings.ntfy_projects_enabled:
-                await _dispatch_projects(db, settings, today)
+            for user_settings in all_settings:
+                try:
+                    await _dispatch_for_user(db, user_settings, now)
+                except Exception:
+                    # Isolate per-user failures — log and continue to next user
+                    logger.exception(
+                        "ntfy dispatch failed for user_id=%s", user_settings.user_id
+                    )
 
-            # Daily housekeeping: purge stale dedup records
+            # Daily housekeeping: purge stale dedup records (shared across all users)
             await _purge_old_sent_records(db)
 
         # Security housekeeping runs every cycle regardless of ntfy_enabled
diff --git a/backend/app/main.py b/backend/app/main.py
index c3a7e9a..624a61f 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -7,7 +7,7 @@ from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from app.config import settings
 from app.database import engine
 from app.routers import auth, todos, events, calendars, reminders, projects, people, locations, settings as settings_router, dashboard, weather, event_templates
-from app.routers import totp
+from app.routers import totp, admin
 from app.jobs.notifications import run_notification_dispatch
 
 # Import models so Alembic's autogenerate can discover them
@@ -15,6 +15,8 @@ from app.models import user as _user_model  # noqa: F401
 from app.models import session as _session_model  # noqa: F401
 from app.models import totp_usage as _totp_usage_model  # noqa: F401
 from app.models import backup_code as _backup_code_model  # noqa: F401
+from app.models import system_config as _system_config_model  # noqa: F401
+from app.models import audit_log as _audit_log_model  # noqa: F401
 
 
 @asynccontextmanager
@@ -68,6 +70,7 @@ app.include_router(dashboard.router, prefix="/api", tags=["Dashboard"])
 app.include_router(weather.router, prefix="/api/weather", tags=["Weather"])
 app.include_router(event_templates.router, prefix="/api/event-templates", tags=["Event Templates"])
 app.include_router(totp.router, prefix="/api/auth", tags=["TOTP MFA"])
+app.include_router(admin.router, prefix="/api/admin", tags=["Admin"])
 
 
 @app.get("/")
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
index cca74b0..d9d7a34 100644
--- a/backend/app/models/__init__.py
+++ b/backend/app/models/__init__.py
@@ -13,6 +13,8 @@ from app.models.session import UserSession
 from app.models.ntfy_sent import NtfySent
 from app.models.totp_usage import TOTPUsage
 from app.models.backup_code import BackupCode
+from app.models.system_config import SystemConfig
+from app.models.audit_log import AuditLog
 
 __all__ = [
     "Settings",
@@ -30,4 +32,6 @@ __all__ = [
     "NtfySent",
     "TOTPUsage",
     "BackupCode",
+    "SystemConfig",
+    "AuditLog",
 ]
diff --git a/backend/app/models/audit_log.py b/backend/app/models/audit_log.py
new file mode 100644
index 0000000..a16f8a6
--- /dev/null
+++ b/backend/app/models/audit_log.py
@@ -0,0 +1,27 @@
+from sqlalchemy import String, Text, Integer, ForeignKey, func
+from sqlalchemy.orm import Mapped, mapped_column
+from datetime import datetime
+from typing import Optional
+from app.database import Base
+
+
+class AuditLog(Base):
+    """
+    Append-only audit trail for admin actions and auth events.
+    No DELETE endpoint — this table is immutable once written.
+    """
+    __tablename__ = "audit_log"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    actor_user_id: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id"), nullable=True, index=True
+    )
+    target_user_id: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    action: Mapped[str] = mapped_column(String(100), nullable=False, index=True)
+    detail: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
+    ip_address: Mapped[Optional[str]] = mapped_column(String(45), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(
+        default=func.now(), server_default=func.now(), index=True
+    )
diff --git a/backend/app/models/calendar.py b/backend/app/models/calendar.py
index 60de5f7..43ab782 100644
--- a/backend/app/models/calendar.py
+++ b/backend/app/models/calendar.py
@@ -1,4 +1,4 @@
-from sqlalchemy import String, Boolean, func
+from sqlalchemy import String, Boolean, Integer, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from datetime import datetime
 from typing import List
@@ -9,6 +9,9 @@ class Calendar(Base):
     __tablename__ = "calendars"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     name: Mapped[str] = mapped_column(String(100), nullable=False)
     color: Mapped[str] = mapped_column(String(20), nullable=False, default="#3b82f6")
     is_default: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
diff --git a/backend/app/models/event_template.py b/backend/app/models/event_template.py
index 47004de..78f8a2d 100644
--- a/backend/app/models/event_template.py
+++ b/backend/app/models/event_template.py
@@ -9,6 +9,9 @@ class EventTemplate(Base):
     __tablename__ = "event_templates"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     title: Mapped[str] = mapped_column(String(255), nullable=False)
     description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
diff --git a/backend/app/models/location.py b/backend/app/models/location.py
index 7dbea4a..c78adf8 100644
--- a/backend/app/models/location.py
+++ b/backend/app/models/location.py
@@ -1,4 +1,4 @@
-from sqlalchemy import String, Text, Boolean, func, text
+from sqlalchemy import String, Text, Boolean, Integer, ForeignKey, func, text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from datetime import datetime
 from typing import Optional, List
@@ -9,6 +9,9 @@ class Location(Base):
     __tablename__ = "locations"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     address: Mapped[str] = mapped_column(Text, nullable=False)
     category: Mapped[str] = mapped_column(String(100), default="other")
diff --git a/backend/app/models/ntfy_sent.py b/backend/app/models/ntfy_sent.py
index ad3868a..a819741 100644
--- a/backend/app/models/ntfy_sent.py
+++ b/backend/app/models/ntfy_sent.py
@@ -1,4 +1,4 @@
-from sqlalchemy import String, func
+from sqlalchemy import String, Integer, ForeignKey, UniqueConstraint, func
 from sqlalchemy.orm import Mapped, mapped_column
 from datetime import datetime
 from app.database import Base
@@ -8,7 +8,7 @@ class NtfySent(Base):
     """
     Deduplication table for ntfy notifications.
     Prevents the background job from re-sending the same notification
-    within a given time window.
+    within a given time window. Scoped per-user.
 
     Key format: "{type}:{entity_id}:{date_window}"
     Examples:
@@ -18,7 +18,13 @@ class NtfySent(Base):
       "project:3:2026-02-25"
     """
     __tablename__ = "ntfy_sent"
+    __table_args__ = (
+        UniqueConstraint("user_id", "notification_key", name="uq_ntfy_sent_user_key"),
+    )
 
     id: Mapped[int] = mapped_column(primary_key=True)
-    notification_key: Mapped[str] = mapped_column(String(255), unique=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    notification_key: Mapped[str] = mapped_column(String(255), index=True)
     sent_at: Mapped[datetime] = mapped_column(default=func.now(), server_default=func.now())
diff --git a/backend/app/models/person.py b/backend/app/models/person.py
index fbf7984..66c3acd 100644
--- a/backend/app/models/person.py
+++ b/backend/app/models/person.py
@@ -1,4 +1,4 @@
-from sqlalchemy import String, Text, Date, Boolean, func, text
+from sqlalchemy import String, Text, Date, Boolean, Integer, ForeignKey, func, text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from datetime import datetime, date
 from typing import Optional, List
@@ -9,6 +9,9 @@ class Person(Base):
     __tablename__ = "people"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     email: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
     phone: Mapped[Optional[str]] = mapped_column(String(50), nullable=True)
diff --git a/backend/app/models/project.py b/backend/app/models/project.py
index 57b0969..faefbe5 100644
--- a/backend/app/models/project.py
+++ b/backend/app/models/project.py
@@ -1,5 +1,5 @@
 import sqlalchemy as sa
-from sqlalchemy import Boolean, String, Text, Date, func
+from sqlalchemy import Boolean, String, Text, Date, Integer, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from datetime import datetime, date
 from typing import Optional, List
@@ -10,6 +10,9 @@ class Project(Base):
     __tablename__ = "projects"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
     status: Mapped[str] = mapped_column(String(20), default="not_started")
diff --git a/backend/app/models/reminder.py b/backend/app/models/reminder.py
index 8259d21..261a89b 100644
--- a/backend/app/models/reminder.py
+++ b/backend/app/models/reminder.py
@@ -1,4 +1,4 @@
-from sqlalchemy import String, Text, Boolean, func
+from sqlalchemy import String, Text, Boolean, Integer, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column
 from datetime import datetime
 from typing import Optional
@@ -9,6 +9,9 @@ class Reminder(Base):
     __tablename__ = "reminders"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     title: Mapped[str] = mapped_column(String(255), nullable=False)
     description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
     remind_at: Mapped[Optional[datetime]] = mapped_column(nullable=True)
diff --git a/backend/app/models/system_config.py b/backend/app/models/system_config.py
new file mode 100644
index 0000000..3e801b2
--- /dev/null
+++ b/backend/app/models/system_config.py
@@ -0,0 +1,27 @@
+from sqlalchemy import Boolean, CheckConstraint, func
+from sqlalchemy.orm import Mapped, mapped_column
+from datetime import datetime
+from app.database import Base
+
+
+class SystemConfig(Base):
+    """
+    Singleton system configuration table (always id=1).
+    Stores global toggles for registration, MFA enforcement, etc.
+    """
+    __tablename__ = "system_config"
+    __table_args__ = (
+        CheckConstraint("id = 1", name="ck_system_config_singleton"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    allow_registration: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+    enforce_mfa_new_users: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+    created_at: Mapped[datetime] = mapped_column(default=func.now(), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        default=func.now(), onupdate=func.now(), server_default=func.now()
+    )
diff --git a/backend/app/models/todo.py b/backend/app/models/todo.py
index cf38b3f..23850ed 100644
--- a/backend/app/models/todo.py
+++ b/backend/app/models/todo.py
@@ -9,6 +9,9 @@ class Todo(Base):
     __tablename__ = "todos"
 
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
     title: Mapped[str] = mapped_column(String(255), nullable=False)
     description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
     priority: Mapped[str] = mapped_column(String(20), default="medium")
diff --git a/backend/app/models/user.py b/backend/app/models/user.py
index 8de4311..efe582f 100644
--- a/backend/app/models/user.py
+++ b/backend/app/models/user.py
@@ -23,7 +23,23 @@ class User(Base):
     # Account state
     is_active: Mapped[bool] = mapped_column(Boolean, default=True)
 
+    # RBAC
+    role: Mapped[str] = mapped_column(
+        String(30), nullable=False, default="standard", server_default="standard"
+    )
+
+    # MFA enforcement (admin can toggle; checked at login)
+    mfa_enforce_pending: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+
+    # Forced password change (set after admin reset)
+    must_change_password: Mapped[bool] = mapped_column(
+        Boolean, default=False, server_default="false"
+    )
+
     # Audit
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())
     last_login_at: Mapped[datetime | None] = mapped_column(nullable=True, default=None)
+    last_password_change_at: Mapped[datetime | None] = mapped_column(nullable=True, default=None)
diff --git a/backend/app/routers/admin.py b/backend/app/routers/admin.py
new file mode 100644
index 0000000..7c80b1a
--- /dev/null
+++ b/backend/app/routers/admin.py
@@ -0,0 +1,687 @@
+"""
+Admin router — full user management, system config, and audit log.
+
+Security measures implemented:
+  SEC-02: Session revocation on role change
+  SEC-05: Block admin self-actions (own role/password/MFA/active status)
+  SEC-08: X-Requested-With header check (verify_xhr) on all state-mutating requests
+  SEC-13: Session revocation + ntfy alert on MFA disable
+
+All routes require the `require_admin` dependency (which chains through
+get_current_user, so the session cookie is always validated).
+"""
+import secrets
+from datetime import datetime
+from typing import Optional
+
+import sqlalchemy as sa
+from fastapi import APIRouter, Depends, HTTPException, Query, Request
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.models.audit_log import AuditLog
+from app.models.backup_code import BackupCode
+from app.models.session import UserSession
+from app.models.system_config import SystemConfig
+from app.models.user import User
+from app.routers.auth import (
+    _create_user_defaults,
+    get_current_user,
+    require_admin,
+)
+from app.schemas.admin import (
+    AdminDashboardResponse,
+    AuditLogEntry,
+    AuditLogResponse,
+    CreateUserRequest,
+    ResetPasswordResponse,
+    SystemConfigResponse,
+    SystemConfigUpdate,
+    ToggleActiveRequest,
+    ToggleMfaEnforceRequest,
+    UpdateUserRoleRequest,
+    UserDetailResponse,
+    UserListItem,
+    UserListResponse,
+)
+from app.services.audit import log_audit_event
+from app.services.auth import hash_password
+
+# ---------------------------------------------------------------------------
+# CSRF guard — SEC-08
+# ---------------------------------------------------------------------------
+
+async def verify_xhr(request: Request) -> None:
+    """
+    Lightweight CSRF mitigation: require X-Requested-With on state-mutating
+    requests. Browsers never send this header cross-origin without CORS
+    pre-flight, which our CORS policy blocks.
+    """
+    if request.method not in ("GET", "HEAD", "OPTIONS"):
+        if request.headers.get("X-Requested-With") != "XMLHttpRequest":
+            raise HTTPException(status_code=403, detail="Invalid request origin")
+
+
+# ---------------------------------------------------------------------------
+# Router — all endpoints inherit require_admin + verify_xhr
+# ---------------------------------------------------------------------------
+
+router = APIRouter(
+    dependencies=[Depends(require_admin), Depends(verify_xhr)],
+)
+
+
+# ---------------------------------------------------------------------------
+# Session revocation helper (used in multiple endpoints)
+# ---------------------------------------------------------------------------
+
+async def _revoke_all_sessions(db: AsyncSession, user_id: int) -> int:
+    """Mark every active session for user_id as revoked. Returns count revoked."""
+    result = await db.execute(
+        sa.update(UserSession)
+        .where(UserSession.user_id == user_id, UserSession.revoked == False)
+        .values(revoked=True)
+        .returning(UserSession.id)
+    )
+    return len(result.fetchall())
+
+
+# ---------------------------------------------------------------------------
+# Self-action guard — SEC-05
+# ---------------------------------------------------------------------------
+
+def _guard_self_action(actor: User, target_id: int, action: str) -> None:
+    """Raise 403 if an admin attempts a privileged action against their own account."""
+    if actor.id == target_id:
+        raise HTTPException(
+            status_code=403,
+            detail=f"Admins cannot {action} their own account",
+        )
+
+
+# ---------------------------------------------------------------------------
+# GET /users
+# ---------------------------------------------------------------------------
+
+@router.get("/users", response_model=UserListResponse)
+async def list_users(
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+):
+    """Return all users with basic stats."""
+    result = await db.execute(sa.select(User).order_by(User.created_at))
+    users = result.scalars().all()
+    return UserListResponse(
+        users=[UserListItem.model_validate(u) for u in users],
+        total=len(users),
+    )
+
+
+# ---------------------------------------------------------------------------
+# GET /users/{user_id}
+# ---------------------------------------------------------------------------
+
+@router.get("/users/{user_id}", response_model=UserDetailResponse)
+async def get_user(
+    user_id: int,
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+):
+    """Return a single user with their active session count."""
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    session_result = await db.execute(
+        sa.select(sa.func.count()).select_from(UserSession).where(
+            UserSession.user_id == user_id,
+            UserSession.revoked == False,
+            UserSession.expires_at > datetime.now(),
+        )
+    )
+    active_sessions = session_result.scalar_one()
+
+    return UserDetailResponse(
+        **UserListItem.model_validate(user).model_dump(),
+        active_sessions=active_sessions,
+    )
+
+
+# ---------------------------------------------------------------------------
+# POST /users
+# ---------------------------------------------------------------------------
+
+@router.post("/users", response_model=UserDetailResponse, status_code=201)
+async def create_user(
+    data: CreateUserRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """Admin-create a user with Settings and default calendars."""
+    existing = await db.execute(sa.select(User).where(User.username == data.username))
+    if existing.scalar_one_or_none():
+        raise HTTPException(status_code=409, detail="Username already taken")
+
+    new_user = User(
+        username=data.username,
+        password_hash=hash_password(data.password),
+        role=data.role,
+        last_password_change_at=datetime.now(),
+        # Force password change so the user sets their own credential
+        must_change_password=True,
+    )
+    db.add(new_user)
+    await db.flush()  # populate new_user.id
+
+    await _create_user_defaults(db, new_user.id)
+    await db.commit()
+
+    await log_audit_event(
+        db,
+        action="admin.user_created",
+        actor_id=actor.id,
+        target_id=new_user.id,
+        detail={"username": new_user.username, "role": new_user.role},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    return UserDetailResponse(
+        **UserListItem.model_validate(new_user).model_dump(),
+        active_sessions=0,
+    )
+
+
+# ---------------------------------------------------------------------------
+# PUT /users/{user_id}/role — SEC-02, SEC-05
+# ---------------------------------------------------------------------------
+
+@router.put("/users/{user_id}/role")
+async def update_user_role(
+    user_id: int,
+    data: UpdateUserRoleRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """
+    Change a user's role.
+    Blocks demotion of the last admin (SEC-05 variant).
+    Revokes all sessions after role change (SEC-02).
+    """
+    _guard_self_action(actor, user_id, "change role of")
+
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    # Prevent demoting the last admin
+    if user.role == "admin" and data.role != "admin":
+        admin_count = await db.scalar(
+            sa.select(sa.func.count()).select_from(User).where(User.role == "admin")
+        )
+        if admin_count <= 1:
+            raise HTTPException(
+                status_code=409,
+                detail="Cannot demote the last admin account",
+            )
+
+    old_role = user.role
+    user.role = data.role
+
+    # SEC-02: revoke sessions so the new role takes effect immediately
+    revoked = await _revoke_all_sessions(db, user_id)
+
+    await log_audit_event(
+        db,
+        action="admin.role_changed",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"old_role": old_role, "new_role": data.role, "sessions_revoked": revoked},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    return {"message": f"Role updated to '{data.role}'. {revoked} session(s) revoked."}
+
+
+# ---------------------------------------------------------------------------
+# POST /users/{user_id}/reset-password — SEC-05
+# ---------------------------------------------------------------------------
+
+@router.post("/users/{user_id}/reset-password", response_model=ResetPasswordResponse)
+async def reset_user_password(
+    user_id: int,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """
+    Generate a temporary password, revoke all sessions, and mark must_change_password.
+    The admin is shown the plaintext temp password once — it is not stored.
+    """
+    _guard_self_action(actor, user_id, "reset the password of")
+
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    temp_password = secrets.token_urlsafe(16)
+    user.password_hash = hash_password(temp_password)
+    user.must_change_password = True
+    user.last_password_change_at = datetime.now()
+
+    revoked = await _revoke_all_sessions(db, user_id)
+
+    await log_audit_event(
+        db,
+        action="admin.password_reset",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"sessions_revoked": revoked},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    return ResetPasswordResponse(
+        message=f"Password reset. {revoked} session(s) revoked. User must change password on next login.",
+        temporary_password=temp_password,
+    )
+
+
+# ---------------------------------------------------------------------------
+# POST /users/{user_id}/disable-mfa — SEC-05, SEC-13
+# ---------------------------------------------------------------------------
+
+@router.post("/users/{user_id}/disable-mfa")
+async def disable_user_mfa(
+    user_id: int,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """
+    Clear TOTP secret + backup codes and revoke all sessions (SEC-13).
+    """
+    _guard_self_action(actor, user_id, "disable MFA for")
+
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    if not user.totp_enabled:
+        raise HTTPException(status_code=409, detail="MFA is not enabled for this user")
+
+    # Clear TOTP data
+    user.totp_secret = None
+    user.totp_enabled = False
+    user.mfa_enforce_pending = False
+
+    # Remove all backup codes
+    await db.execute(
+        sa.delete(BackupCode).where(BackupCode.user_id == user_id)
+    )
+
+    # SEC-13: revoke sessions so the MFA downgrade takes effect immediately
+    revoked = await _revoke_all_sessions(db, user_id)
+
+    await log_audit_event(
+        db,
+        action="admin.mfa_disabled",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"sessions_revoked": revoked},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    return {"message": f"MFA disabled. {revoked} session(s) revoked."}
+
+
+# ---------------------------------------------------------------------------
+# PUT /users/{user_id}/enforce-mfa — SEC-05
+# ---------------------------------------------------------------------------
+
+@router.put("/users/{user_id}/enforce-mfa")
+async def toggle_mfa_enforce(
+    user_id: int,
+    data: ToggleMfaEnforceRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """Toggle the mfa_enforce_pending flag. Next login will prompt MFA setup."""
+    _guard_self_action(actor, user_id, "toggle MFA enforcement for")
+
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    user.mfa_enforce_pending = data.enforce
+
+    await log_audit_event(
+        db,
+        action="admin.mfa_enforce_toggled",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"enforce": data.enforce},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    return {"message": f"MFA enforcement {'enabled' if data.enforce else 'disabled'} for user."}
+
+
+# ---------------------------------------------------------------------------
+# PUT /users/{user_id}/active — SEC-05
+# ---------------------------------------------------------------------------
+
+@router.put("/users/{user_id}/active")
+async def toggle_user_active(
+    user_id: int,
+    data: ToggleActiveRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """
+    Enable or disable a user account.
+    Revoking an account also revokes all active sessions immediately.
+    """
+    _guard_self_action(actor, user_id, "change active status of")
+
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    user.is_active = data.is_active
+    revoked = 0
+
+    if not data.is_active:
+        revoked = await _revoke_all_sessions(db, user_id)
+
+    await log_audit_event(
+        db,
+        action="admin.user_deactivated" if not data.is_active else "admin.user_activated",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"sessions_revoked": revoked},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    state = "activated" if data.is_active else f"deactivated ({revoked} session(s) revoked)"
+    return {"message": f"User {state}."}
+
+
+# ---------------------------------------------------------------------------
+# DELETE /users/{user_id}/sessions
+# ---------------------------------------------------------------------------
+
+@router.delete("/users/{user_id}/sessions")
+async def revoke_user_sessions(
+    user_id: int,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """Forcibly revoke all active sessions for a user."""
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    if not result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="User not found")
+
+    revoked = await _revoke_all_sessions(db, user_id)
+
+    await log_audit_event(
+        db,
+        action="admin.sessions_revoked",
+        actor_id=actor.id,
+        target_id=user_id,
+        detail={"sessions_revoked": revoked},
+        ip=request.client.host if request.client else None,
+    )
+    await db.commit()
+
+    return {"message": f"{revoked} session(s) revoked."}
+
+
+# ---------------------------------------------------------------------------
+# GET /users/{user_id}/sessions
+# ---------------------------------------------------------------------------
+
+@router.get("/users/{user_id}/sessions")
+async def list_user_sessions(
+    user_id: int,
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+):
+    """List all active (non-revoked, non-expired) sessions for a user."""
+    result = await db.execute(sa.select(User).where(User.id == user_id))
+    if not result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="User not found")
+
+    sessions_result = await db.execute(
+        sa.select(UserSession).where(
+            UserSession.user_id == user_id,
+            UserSession.revoked == False,
+            UserSession.expires_at > datetime.now(),
+        ).order_by(UserSession.created_at.desc())
+    )
+    sessions = sessions_result.scalars().all()
+
+    return {
+        "sessions": [
+            {
+                "id": s.id,
+                "created_at": s.created_at,
+                "expires_at": s.expires_at,
+                "ip_address": s.ip_address,
+                "user_agent": s.user_agent,
+            }
+            for s in sessions
+        ],
+        "total": len(sessions),
+    }
+
+
+# ---------------------------------------------------------------------------
+# GET /config
+# ---------------------------------------------------------------------------
+
+@router.get("/config", response_model=SystemConfigResponse)
+async def get_system_config(
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+):
+    """Fetch the singleton system configuration row."""
+    result = await db.execute(sa.select(SystemConfig).where(SystemConfig.id == 1))
+    config = result.scalar_one_or_none()
+    if not config:
+        # Bootstrap the singleton if it doesn't exist yet
+        config = SystemConfig(id=1)
+        db.add(config)
+        await db.commit()
+    return config
+
+
+# ---------------------------------------------------------------------------
+# PUT /config
+# ---------------------------------------------------------------------------
+
+@router.put("/config", response_model=SystemConfigResponse)
+async def update_system_config(
+    data: SystemConfigUpdate,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+    actor: User = Depends(get_current_user),
+):
+    """Update one or more system config fields (partial update)."""
+    result = await db.execute(sa.select(SystemConfig).where(SystemConfig.id == 1))
+    config = result.scalar_one_or_none()
+    if not config:
+        config = SystemConfig(id=1)
+        db.add(config)
+        await db.flush()
+
+    changes: dict = {}
+    if data.allow_registration is not None:
+        changes["allow_registration"] = data.allow_registration
+        config.allow_registration = data.allow_registration
+    if data.enforce_mfa_new_users is not None:
+        changes["enforce_mfa_new_users"] = data.enforce_mfa_new_users
+        config.enforce_mfa_new_users = data.enforce_mfa_new_users
+
+    if changes:
+        await log_audit_event(
+            db,
+            action="admin.config_updated",
+            actor_id=actor.id,
+            detail=changes,
+            ip=request.client.host if request.client else None,
+        )
+
+    await db.commit()
+    return config
+
+
+# ---------------------------------------------------------------------------
+# GET /dashboard
+# ---------------------------------------------------------------------------
+
+@router.get("/dashboard", response_model=AdminDashboardResponse)
+async def admin_dashboard(
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+):
+    """Aggregate stats for the admin portal dashboard."""
+    total_users = await db.scalar(
+        sa.select(sa.func.count()).select_from(User)
+    )
+    active_users = await db.scalar(
+        sa.select(sa.func.count()).select_from(User).where(User.is_active == True)
+    )
+    admin_count = await db.scalar(
+        sa.select(sa.func.count()).select_from(User).where(User.role == "admin")
+    )
+    totp_count = await db.scalar(
+        sa.select(sa.func.count()).select_from(User).where(User.totp_enabled == True)
+    )
+    active_sessions = await db.scalar(
+        sa.select(sa.func.count()).select_from(UserSession).where(
+            UserSession.revoked == False,
+            UserSession.expires_at > datetime.now(),
+        )
+    )
+
+    mfa_adoption = (totp_count / total_users) if total_users else 0.0
+
+    # 10 most recent logins — join to get username
+    actor_alias = sa.alias(User.__table__, name="actor")
+    recent_logins_result = await db.execute(
+        sa.select(User.username, User.last_login_at)
+        .where(User.last_login_at != None)
+        .order_by(User.last_login_at.desc())
+        .limit(10)
+    )
+    recent_logins = [
+        {"username": row.username, "last_login_at": row.last_login_at}
+        for row in recent_logins_result
+    ]
+
+    # 10 most recent audit entries
+    recent_audit_result = await db.execute(
+        sa.select(AuditLog).order_by(AuditLog.created_at.desc()).limit(10)
+    )
+    recent_audit_entries = [
+        {
+            "id": e.id,
+            "action": e.action,
+            "actor_user_id": e.actor_user_id,
+            "target_user_id": e.target_user_id,
+            "detail": e.detail,
+            "created_at": e.created_at,
+        }
+        for e in recent_audit_result.scalars()
+    ]
+
+    return AdminDashboardResponse(
+        total_users=total_users or 0,
+        active_users=active_users or 0,
+        admin_count=admin_count or 0,
+        active_sessions=active_sessions or 0,
+        mfa_adoption_rate=round(mfa_adoption, 4),
+        recent_logins=recent_logins,
+        recent_audit_entries=recent_audit_entries,
+    )
+
+
+# ---------------------------------------------------------------------------
+# GET /audit-log
+# ---------------------------------------------------------------------------
+
+@router.get("/audit-log", response_model=AuditLogResponse)
+async def get_audit_log(
+    db: AsyncSession = Depends(get_db),
+    _actor: User = Depends(get_current_user),
+    action: Optional[str] = Query(None, description="Filter by action string (prefix match)"),
+    target_user_id: Optional[int] = Query(None, description="Filter by target user ID"),
+    page: int = Query(1, ge=1, description="Page number (1-indexed)"),
+    per_page: int = Query(50, ge=1, le=200, description="Results per page"),
+):
+    """
+    Paginated audit log with optional filters.
+    Resolves actor and target user IDs to usernames via a JOIN.
+    """
+    # Aliases for the two user joins
+    actor_user = sa.orm.aliased(User, name="actor_user")
+    target_user = sa.orm.aliased(User, name="target_user")
+
+    # Base query — left outer join so entries with NULL actor/target still appear
+    base_q = (
+        sa.select(
+            AuditLog,
+            actor_user.username.label("actor_username"),
+            target_user.username.label("target_username"),
+        )
+        .outerjoin(actor_user, AuditLog.actor_user_id == actor_user.id)
+        .outerjoin(target_user, AuditLog.target_user_id == target_user.id)
+    )
+
+    if action:
+        base_q = base_q.where(AuditLog.action.like(f"{action}%"))
+    if target_user_id is not None:
+        base_q = base_q.where(AuditLog.target_user_id == target_user_id)
+
+    # Count before pagination
+    count_q = sa.select(sa.func.count()).select_from(
+        base_q.subquery()
+    )
+    total = await db.scalar(count_q) or 0
+
+    # Paginate
+    offset = (page - 1) * per_page
+    rows_result = await db.execute(
+        base_q.order_by(AuditLog.created_at.desc()).offset(offset).limit(per_page)
+    )
+
+    entries = [
+        AuditLogEntry(
+            id=row.AuditLog.id,
+            actor_username=row.actor_username,
+            target_username=row.target_username,
+            action=row.AuditLog.action,
+            detail=row.AuditLog.detail,
+            ip_address=row.AuditLog.ip_address,
+            created_at=row.AuditLog.created_at,
+        )
+        for row in rows_result
+    ]
+
+    return AuditLogResponse(entries=entries, total=total)
diff --git a/backend/app/routers/auth.py b/backend/app/routers/auth.py
index e0fb04b..5dbeac1 100644
--- a/backend/app/routers/auth.py
+++ b/backend/app/routers/auth.py
@@ -1,18 +1,20 @@
 """
-Authentication router — username/password with DB-backed sessions and account lockout.
+Authentication router — username/password with DB-backed sessions, account lockout,
+role-based access control, and multi-user registration.
 
 Session flow:
-  POST /setup  → create User + Settings row → issue session cookie
-  POST /login  → verify credentials → check lockout → insert UserSession → issue cookie
-               → if TOTP enabled: return mfa_token instead of full session
+  POST /setup  → create admin User + Settings + calendars → issue session cookie
+  POST /login  → verify credentials → check lockout → MFA/enforce checks → issue session
+  POST /register → create standard user (when registration enabled)
   POST /logout → mark session revoked in DB → delete cookie
-  GET  /status → verify user exists + session valid
+  GET  /status → verify user exists + session valid + role + registration_open
 
 Security layers:
-  1. Nginx limit_req_zone (real-IP, 10 req/min burst 5) — outer guard on all auth endpoints
-  2. DB-backed account lockout (10 failures → 30-min lock, HTTP 423) — per-user guard
+  1. Nginx limit_req_zone (real-IP, 10 req/min burst 5) — outer guard on auth endpoints
+  2. DB-backed account lockout (10 failures → 30-min lock, HTTP 423)
   3. Session revocation stored in DB (survives container restarts)
-  4. bcrypt→Argon2id transparent upgrade on first login with migrated hash
+  4. bcrypt→Argon2id transparent upgrade on first login
+  5. Role-based authorization via require_role() dependency factory
 """
 import uuid
 from datetime import datetime, timedelta
@@ -26,14 +28,21 @@ from app.database import get_db
 from app.models.user import User
 from app.models.session import UserSession
 from app.models.settings import Settings
-from app.schemas.auth import SetupRequest, LoginRequest, ChangePasswordRequest, VerifyPasswordRequest
+from app.models.system_config import SystemConfig
+from app.models.calendar import Calendar
+from app.schemas.auth import (
+    SetupRequest, LoginRequest, RegisterRequest,
+    ChangePasswordRequest, VerifyPasswordRequest,
+)
 from app.services.auth import (
     hash_password,
     verify_password_with_upgrade,
     create_session_token,
     verify_session_token,
     create_mfa_token,
+    create_mfa_enforce_token,
 )
+from app.services.audit import log_audit_event
 from app.config import settings as app_settings
 
 router = APIRouter()
@@ -64,8 +73,6 @@ async def get_current_user(
 ) -> User:
     """
     Dependency that verifies the session cookie and returns the authenticated User.
-    Replaces the old get_current_session (which returned Settings).
-    Any router that hasn't been updated will get a compile-time type error.
     """
     if not session_cookie:
         raise HTTPException(status_code=401, detail="Not authenticated")
@@ -119,6 +126,24 @@ async def get_current_settings(
     return settings_obj
 
 
+# ---------------------------------------------------------------------------
+# Role-based authorization dependencies
+# ---------------------------------------------------------------------------
+
+def require_role(*allowed_roles: str):
+    """Factory: returns a dependency that enforces role membership."""
+    async def _check(
+        current_user: User = Depends(get_current_user),
+    ) -> User:
+        if current_user.role not in allowed_roles:
+            raise HTTPException(status_code=403, detail="Insufficient permissions")
+        return current_user
+    return _check
+
+# Convenience aliases
+require_admin = require_role("admin")
+
+
 # ---------------------------------------------------------------------------
 # Account lockout helpers
 # ---------------------------------------------------------------------------
@@ -166,7 +191,7 @@ async def _create_db_session(
         id=session_id,
         user_id=user.id,
         expires_at=expires_at,
-        ip_address=ip[:45] if ip else None,  # clamp to column width
+        ip_address=ip[:45] if ip else None,
         user_agent=(user_agent or "")[:255] if user_agent else None,
     )
     db.add(db_session)
@@ -175,6 +200,25 @@ async def _create_db_session(
     return session_id, token
 
 
+# ---------------------------------------------------------------------------
+# User bootstrapping helper (Settings + default calendars)
+# ---------------------------------------------------------------------------
+
+async def _create_user_defaults(db: AsyncSession, user_id: int) -> None:
+    """Create Settings row and default calendars for a new user."""
+    db.add(Settings(user_id=user_id))
+    db.add(Calendar(
+        name="Personal", color="#3b82f6",
+        is_default=True, is_system=False, is_visible=True,
+        user_id=user_id,
+    ))
+    db.add(Calendar(
+        name="Birthdays", color="#f59e0b",
+        is_default=False, is_system=True, is_visible=True,
+        user_id=user_id,
+    ))
+
+
 # ---------------------------------------------------------------------------
 # Routes
 # ---------------------------------------------------------------------------
@@ -187,7 +231,7 @@ async def setup(
     db: AsyncSession = Depends(get_db),
 ):
     """
-    First-time setup: create the User record and a linked Settings row.
+    First-time setup: create the admin User + Settings + default calendars.
     Only works when no users exist (i.e., fresh install).
     """
     existing = await db.execute(select(User))
@@ -195,13 +239,16 @@ async def setup(
         raise HTTPException(status_code=400, detail="Setup already completed")
 
     password_hash = hash_password(data.password)
-    new_user = User(username=data.username, password_hash=password_hash)
+    new_user = User(
+        username=data.username,
+        password_hash=password_hash,
+        role="admin",
+        last_password_change_at=datetime.now(),
+    )
     db.add(new_user)
-    await db.flush()  # assign new_user.id before creating Settings
+    await db.flush()
 
-    # Create Settings row linked to this user with all defaults
-    new_settings = Settings(user_id=new_user.id)
-    db.add(new_settings)
+    await _create_user_defaults(db, new_user.id)
     await db.commit()
 
     ip = request.client.host if request.client else "unknown"
@@ -209,6 +256,11 @@ async def setup(
     _, token = await _create_db_session(db, new_user, ip, user_agent)
     _set_session_cookie(response, token)
 
+    await log_audit_event(
+        db, action="auth.setup_complete", actor_id=new_user.id, ip=ip,
+    )
+    await db.commit()
+
     return {"message": "Setup completed successfully", "authenticated": True}
 
 
@@ -223,15 +275,15 @@ async def login(
     Authenticate with username + password.
 
     Returns:
-      { authenticated: true }  — on success (no TOTP)
+      { authenticated: true }  — on success (no TOTP, no enforcement)
       { authenticated: false, totp_required: true, mfa_token: "..." }  — TOTP pending
-      HTTP 401  — wrong credentials (generic; never reveals which field is wrong)
+      { authenticated: false, mfa_setup_required: true, mfa_token: "..." }  — MFA enforcement
+      { authenticated: false, must_change_password: true }  — forced password change after admin reset
+      HTTP 401  — wrong credentials
       HTTP 423  — account locked
-      HTTP 429  — IP rate limited
     """
     client_ip = request.client.host if request.client else "unknown"
 
-    # Lookup user — do NOT differentiate "user not found" from "wrong password"
     result = await db.execute(select(User).where(User.username == data.username))
     user = result.scalar_one_or_none()
 
@@ -240,20 +292,36 @@ async def login(
 
     await _check_account_lockout(user)
 
-    # Transparent bcrypt→Argon2id upgrade
     valid, new_hash = verify_password_with_upgrade(data.password, user.password_hash)
 
     if not valid:
         await _record_failed_login(db, user)
+        await log_audit_event(
+            db, action="auth.login_failed", actor_id=user.id,
+            detail={"reason": "invalid_password"}, ip=client_ip,
+        )
+        await db.commit()
         raise HTTPException(status_code=401, detail="Invalid username or password")
 
-    # Persist upgraded hash if migration happened
     if new_hash:
         user.password_hash = new_hash
 
     await _record_successful_login(db, user)
 
-    # If TOTP is enabled, issue a short-lived MFA challenge token instead of a full session
+    # SEC-03: MFA enforcement — block login entirely until MFA setup completes
+    if user.mfa_enforce_pending and not user.totp_enabled:
+        enforce_token = create_mfa_enforce_token(user.id)
+        await log_audit_event(
+            db, action="auth.mfa_enforce_prompted", actor_id=user.id, ip=client_ip,
+        )
+        await db.commit()
+        return {
+            "authenticated": False,
+            "mfa_setup_required": True,
+            "mfa_token": enforce_token,
+        }
+
+    # If TOTP is enabled, issue a short-lived MFA challenge token
     if user.totp_enabled:
         mfa_token = create_mfa_token(user.id)
         return {
@@ -262,13 +330,97 @@ async def login(
             "mfa_token": mfa_token,
         }
 
+    # SEC-12: Forced password change after admin reset
+    if user.must_change_password:
+        # Issue a session but flag the frontend to show password change
+        user_agent = request.headers.get("user-agent")
+        _, token = await _create_db_session(db, user, client_ip, user_agent)
+        _set_session_cookie(response, token)
+        return {
+            "authenticated": True,
+            "must_change_password": True,
+        }
+
     user_agent = request.headers.get("user-agent")
     _, token = await _create_db_session(db, user, client_ip, user_agent)
     _set_session_cookie(response, token)
 
+    await log_audit_event(
+        db, action="auth.login_success", actor_id=user.id, ip=client_ip,
+    )
+    await db.commit()
+
     return {"authenticated": True}
 
 
+@router.post("/register")
+async def register(
+    data: RegisterRequest,
+    response: Response,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+):
+    """
+    Create a new standard user account.
+    Only available when system_config.allow_registration is True.
+    """
+    config_result = await db.execute(
+        select(SystemConfig).where(SystemConfig.id == 1)
+    )
+    config = config_result.scalar_one_or_none()
+    if not config or not config.allow_registration:
+        raise HTTPException(status_code=403, detail="Registration is not available")
+
+    # Check username availability (generic error to prevent enumeration)
+    existing = await db.execute(
+        select(User).where(User.username == data.username)
+    )
+    if existing.scalar_one_or_none():
+        raise HTTPException(status_code=400, detail="Registration failed")
+
+    password_hash = hash_password(data.password)
+    # SEC-01: Explicit field assignment — never **data.model_dump()
+    new_user = User(
+        username=data.username,
+        password_hash=password_hash,
+        role="standard",
+        last_password_change_at=datetime.now(),
+    )
+
+    # Check if MFA enforcement is enabled for new users
+    if config.enforce_mfa_new_users:
+        new_user.mfa_enforce_pending = True
+
+    db.add(new_user)
+    await db.flush()
+
+    await _create_user_defaults(db, new_user.id)
+    await db.commit()
+
+    ip = request.client.host if request.client else "unknown"
+    user_agent = request.headers.get("user-agent")
+
+    await log_audit_event(
+        db, action="auth.registration", actor_id=new_user.id, ip=ip,
+    )
+    await db.commit()
+
+    # If MFA enforcement is pending, don't issue a session — require MFA setup first
+    if new_user.mfa_enforce_pending:
+        enforce_token = create_mfa_enforce_token(new_user.id)
+        return {
+            "message": "Registration successful",
+            "authenticated": False,
+            "mfa_setup_required": True,
+            "mfa_token": enforce_token,
+        }
+
+    _, token = await _create_db_session(db, new_user, ip, user_agent)
+    _set_session_cookie(response, token)
+
+    return {"message": "Registration successful", "authenticated": True}
+
+
 @router.post("/logout")
 async def logout(
     response: Response,
@@ -304,13 +456,13 @@ async def auth_status(
     db: AsyncSession = Depends(get_db),
 ):
     """
-    Check authentication status and whether initial setup has been performed.
-    Used by the frontend to decide whether to show login vs setup screen.
+    Check authentication status, role, and whether initial setup/registration is available.
     """
     user_result = await db.execute(select(User))
     existing_user = user_result.scalar_one_or_none()
     setup_required = existing_user is None
     authenticated = False
+    role = None
 
     if not setup_required and session_cookie:
         payload = verify_session_token(session_cookie)
@@ -326,9 +478,32 @@ async def auth_status(
                         UserSession.expires_at > datetime.now(),
                     )
                 )
-                authenticated = session_result.scalar_one_or_none() is not None
+                if session_result.scalar_one_or_none() is not None:
+                    authenticated = True
+                    user_obj_result = await db.execute(
+                        select(User).where(User.id == user_id, User.is_active == True)
+                    )
+                    u = user_obj_result.scalar_one_or_none()
+                    if u:
+                        role = u.role
+                    else:
+                        authenticated = False
 
-    return {"authenticated": authenticated, "setup_required": setup_required}
+    # Check registration availability
+    registration_open = False
+    if not setup_required:
+        config_result = await db.execute(
+            select(SystemConfig).where(SystemConfig.id == 1)
+        )
+        config = config_result.scalar_one_or_none()
+        registration_open = config.allow_registration if config else False
+
+    return {
+        "authenticated": authenticated,
+        "setup_required": setup_required,
+        "role": role,
+        "registration_open": registration_open,
+    }
 
 
 @router.post("/verify-password")
@@ -340,8 +515,6 @@ async def verify_password(
     """
     Verify the current user's password without changing anything.
     Used by the frontend lock screen to re-authenticate without a full login.
-    Also handles transparent bcrypt→Argon2id upgrade.
-    Shares the same lockout guards as /login. Nginx limit_req_zone handles IP rate limiting.
     """
     await _check_account_lockout(current_user)
 
@@ -350,7 +523,6 @@ async def verify_password(
         await _record_failed_login(db, current_user)
         raise HTTPException(status_code=401, detail="Invalid password")
 
-    # Persist upgraded hash if migration happened
     if new_hash:
         current_user.password_hash = new_hash
         await db.commit()
@@ -373,6 +545,12 @@ async def change_password(
         raise HTTPException(status_code=401, detail="Invalid current password")
 
     current_user.password_hash = hash_password(data.new_password)
+    current_user.last_password_change_at = datetime.now()
+
+    # Clear forced password change flag if set (SEC-12)
+    if current_user.must_change_password:
+        current_user.must_change_password = False
+
     await db.commit()
 
     return {"message": "Password changed successfully"}
diff --git a/backend/app/routers/calendars.py b/backend/app/routers/calendars.py
index 70322ed..4f35984 100644
--- a/backend/app/routers/calendars.py
+++ b/backend/app/routers/calendars.py
@@ -18,7 +18,11 @@ async def get_calendars(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    result = await db.execute(select(Calendar).order_by(Calendar.is_default.desc(), Calendar.name.asc()))
+    result = await db.execute(
+        select(Calendar)
+        .where(Calendar.user_id == current_user.id)
+        .order_by(Calendar.is_default.desc(), Calendar.name.asc())
+    )
     return result.scalars().all()
 
 
@@ -34,6 +38,7 @@ async def create_calendar(
         is_default=False,
         is_system=False,
         is_visible=True,
+        user_id=current_user.id,
     )
     db.add(new_calendar)
     await db.commit()
@@ -48,7 +53,9 @@ async def update_calendar(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    result = await db.execute(select(Calendar).where(Calendar.id == calendar_id))
+    result = await db.execute(
+        select(Calendar).where(Calendar.id == calendar_id, Calendar.user_id == current_user.id)
+    )
     calendar = result.scalar_one_or_none()
 
     if not calendar:
@@ -74,7 +81,9 @@ async def delete_calendar(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user)
 ):
-    result = await db.execute(select(Calendar).where(Calendar.id == calendar_id))
+    result = await db.execute(
+        select(Calendar).where(Calendar.id == calendar_id, Calendar.user_id == current_user.id)
+    )
     calendar = result.scalar_one_or_none()
 
     if not calendar:
@@ -86,8 +95,13 @@ async def delete_calendar(
     if calendar.is_default:
         raise HTTPException(status_code=400, detail="Cannot delete the default calendar")
 
-    # Reassign all events on this calendar to the default calendar
-    default_result = await db.execute(select(Calendar).where(Calendar.is_default == True))
+    # Reassign all events on this calendar to the user's default calendar
+    default_result = await db.execute(
+        select(Calendar).where(
+            Calendar.user_id == current_user.id,
+            Calendar.is_default == True,
+        )
+    )
     default_calendar = default_result.scalar_one_or_none()
 
     if default_calendar:
diff --git a/backend/app/routers/dashboard.py b/backend/app/routers/dashboard.py
index cd0b8b0..c3b3bbc 100644
--- a/backend/app/routers/dashboard.py
+++ b/backend/app/routers/dashboard.py
@@ -8,9 +8,11 @@ from app.database import get_db
 from app.models.settings import Settings
 from app.models.todo import Todo
 from app.models.calendar_event import CalendarEvent
+from app.models.calendar import Calendar
 from app.models.reminder import Reminder
 from app.models.project import Project
-from app.routers.auth import get_current_settings
+from app.models.user import User
+from app.routers.auth import get_current_user, get_current_settings
 
 router = APIRouter()
 
@@ -26,16 +28,21 @@ _not_parent_template = or_(
 async def get_dashboard(
     client_date: Optional[date] = Query(None),
     db: AsyncSession = Depends(get_db),
-    current_settings: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
+    current_settings: Settings = Depends(get_current_settings),
 ):
     """Get aggregated dashboard data."""
     today = client_date or date.today()
     upcoming_cutoff = today + timedelta(days=current_settings.upcoming_days)
 
+    # Subquery: calendar IDs belonging to this user (for event scoping)
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+
     # Today's events (exclude parent templates — they are hidden, children are shown)
     today_start = datetime.combine(today, datetime.min.time())
     today_end = datetime.combine(today, datetime.max.time())
     events_query = select(CalendarEvent).where(
+        CalendarEvent.calendar_id.in_(user_calendar_ids),
         CalendarEvent.start_datetime >= today_start,
         CalendarEvent.start_datetime <= today_end,
         _not_parent_template,
@@ -45,6 +52,7 @@ async def get_dashboard(
 
     # Upcoming todos (not completed, with due date from today through upcoming_days)
     todos_query = select(Todo).where(
+        Todo.user_id == current_user.id,
         Todo.completed == False,
         Todo.due_date.isnot(None),
         Todo.due_date >= today,
@@ -55,6 +63,7 @@ async def get_dashboard(
 
     # Active reminders (not dismissed, is_active = true, from today onward)
     reminders_query = select(Reminder).where(
+        Reminder.user_id == current_user.id,
         Reminder.is_active == True,
         Reminder.is_dismissed == False,
         Reminder.remind_at >= today_start
@@ -62,26 +71,32 @@ async def get_dashboard(
     reminders_result = await db.execute(reminders_query)
     active_reminders = reminders_result.scalars().all()
 
-    # Project stats
-    total_projects_result = await db.execute(select(func.count(Project.id)))
+    # Project stats (scoped to user)
+    total_projects_result = await db.execute(
+        select(func.count(Project.id)).where(Project.user_id == current_user.id)
+    )
     total_projects = total_projects_result.scalar()
 
     projects_by_status_query = select(
         Project.status,
         func.count(Project.id).label("count")
-    ).group_by(Project.status)
+    ).where(Project.user_id == current_user.id).group_by(Project.status)
     projects_by_status_result = await db.execute(projects_by_status_query)
     projects_by_status = {row[0]: row[1] for row in projects_by_status_result}
 
-    # Total incomplete todos count
+    # Total incomplete todos count (scoped to user)
     total_incomplete_result = await db.execute(
-        select(func.count(Todo.id)).where(Todo.completed == False)
+        select(func.count(Todo.id)).where(
+            Todo.user_id == current_user.id,
+            Todo.completed == False,
+        )
     )
     total_incomplete_todos = total_incomplete_result.scalar()
 
-    # Starred events (upcoming, ordered by date)
+    # Starred events (upcoming, ordered by date, scoped to user's calendars)
     now = datetime.now()
     starred_query = select(CalendarEvent).where(
+        CalendarEvent.calendar_id.in_(user_calendar_ids),
         CalendarEvent.is_starred == True,
         CalendarEvent.start_datetime > now,
         _not_parent_template,
@@ -143,7 +158,8 @@ async def get_upcoming(
     days: int = Query(default=7, ge=1, le=90),
     client_date: Optional[date] = Query(None),
     db: AsyncSession = Depends(get_db),
-    current_settings: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
+    current_settings: Settings = Depends(get_current_settings),
 ):
     """Get unified list of upcoming items (todos, events, reminders) sorted by date."""
     today = client_date or date.today()
@@ -151,8 +167,12 @@ async def get_upcoming(
     cutoff_datetime = datetime.combine(cutoff_date, datetime.max.time())
     today_start = datetime.combine(today, datetime.min.time())
 
-    # Get upcoming todos with due dates (today onward only)
+    # Subquery: calendar IDs belonging to this user
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+
+    # Get upcoming todos with due dates (today onward only, scoped to user)
     todos_query = select(Todo).where(
+        Todo.user_id == current_user.id,
         Todo.completed == False,
         Todo.due_date.isnot(None),
         Todo.due_date >= today,
@@ -161,8 +181,9 @@ async def get_upcoming(
     todos_result = await db.execute(todos_query)
     todos = todos_result.scalars().all()
 
-    # Get upcoming events (from today onward, exclude parent templates)
+    # Get upcoming events (from today onward, exclude parent templates, scoped to user's calendars)
     events_query = select(CalendarEvent).where(
+        CalendarEvent.calendar_id.in_(user_calendar_ids),
         CalendarEvent.start_datetime >= today_start,
         CalendarEvent.start_datetime <= cutoff_datetime,
         _not_parent_template,
@@ -170,8 +191,9 @@ async def get_upcoming(
     events_result = await db.execute(events_query)
     events = events_result.scalars().all()
 
-    # Get upcoming reminders (today onward only)
+    # Get upcoming reminders (today onward only, scoped to user)
     reminders_query = select(Reminder).where(
+        Reminder.user_id == current_user.id,
         Reminder.is_active == True,
         Reminder.is_dismissed == False,
         Reminder.remind_at >= today_start,
diff --git a/backend/app/routers/event_templates.py b/backend/app/routers/event_templates.py
index 95efe42..7d7a90b 100644
--- a/backend/app/routers/event_templates.py
+++ b/backend/app/routers/event_templates.py
@@ -20,7 +20,11 @@ async def list_templates(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    result = await db.execute(select(EventTemplate).order_by(EventTemplate.name))
+    result = await db.execute(
+        select(EventTemplate)
+        .where(EventTemplate.user_id == current_user.id)
+        .order_by(EventTemplate.name)
+    )
     return result.scalars().all()
 
 
@@ -30,7 +34,7 @@ async def create_template(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    template = EventTemplate(**payload.model_dump())
+    template = EventTemplate(**payload.model_dump(), user_id=current_user.id)
     db.add(template)
     await db.commit()
     await db.refresh(template)
@@ -45,7 +49,10 @@ async def update_template(
     current_user: User = Depends(get_current_user),
 ):
     result = await db.execute(
-        select(EventTemplate).where(EventTemplate.id == template_id)
+        select(EventTemplate).where(
+            EventTemplate.id == template_id,
+            EventTemplate.user_id == current_user.id,
+        )
     )
     template = result.scalar_one_or_none()
     if template is None:
@@ -66,7 +73,10 @@ async def delete_template(
     current_user: User = Depends(get_current_user),
 ):
     result = await db.execute(
-        select(EventTemplate).where(EventTemplate.id == template_id)
+        select(EventTemplate).where(
+            EventTemplate.id == template_id,
+            EventTemplate.user_id == current_user.id,
+        )
     )
     template = result.scalar_one_or_none()
     if template is None:
diff --git a/backend/app/routers/events.py b/backend/app/routers/events.py
index d91776f..3dc6e1a 100644
--- a/backend/app/routers/events.py
+++ b/backend/app/routers/events.py
@@ -105,15 +105,29 @@ def _birthday_events_for_range(
     return virtual_events
 
 
-async def _get_default_calendar_id(db: AsyncSession) -> int:
-    """Return the id of the default calendar, raising 500 if not found."""
-    result = await db.execute(select(Calendar).where(Calendar.is_default == True))
+async def _get_default_calendar_id(db: AsyncSession, user_id: int) -> int:
+    """Return the id of the user's default calendar, raising 500 if not found."""
+    result = await db.execute(
+        select(Calendar).where(
+            Calendar.user_id == user_id,
+            Calendar.is_default == True,
+        )
+    )
     default = result.scalar_one_or_none()
     if not default:
         raise HTTPException(status_code=500, detail="No default calendar configured")
     return default.id
 
 
+async def _verify_calendar_ownership(db: AsyncSession, calendar_id: int, user_id: int) -> None:
+    """Raise 404 if calendar_id does not belong to user_id (SEC-04)."""
+    result = await db.execute(
+        select(Calendar).where(Calendar.id == calendar_id, Calendar.user_id == user_id)
+    )
+    if not result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Calendar not found")
+
+
 @router.get("/", response_model=None)
 async def get_events(
     start: Optional[date] = Query(None),
@@ -128,9 +142,13 @@ async def get_events(
     recurrence_rule IS NOT NULL) are excluded — their materialised children
     are what get displayed on the calendar.
     """
+    # Scope events through calendar ownership
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+
     query = (
         select(CalendarEvent)
         .options(selectinload(CalendarEvent.calendar))
+        .where(CalendarEvent.calendar_id.in_(user_calendar_ids))
     )
 
     # Exclude parent template rows — they are not directly rendered
@@ -154,14 +172,24 @@ async def get_events(
 
     response: List[dict] = [_event_to_dict(e) for e in events]
 
-    # Fetch Birthdays calendar; only generate virtual events if visible
+    # Fetch the user's Birthdays system calendar; only generate virtual events if visible
     bday_result = await db.execute(
-        select(Calendar).where(Calendar.name == "Birthdays", Calendar.is_system == True)
+        select(Calendar).where(
+            Calendar.user_id == current_user.id,
+            Calendar.name == "Birthdays",
+            Calendar.is_system == True,
+        )
     )
     bday_calendar = bday_result.scalar_one_or_none()
 
     if bday_calendar and bday_calendar.is_visible:
-        people_result = await db.execute(select(Person).where(Person.birthday.isnot(None)))
+        # Scope birthday people to this user
+        people_result = await db.execute(
+            select(Person).where(
+                Person.user_id == current_user.id,
+                Person.birthday.isnot(None),
+            )
+        )
         people = people_result.scalars().all()
 
         virtual = _birthday_events_for_range(
@@ -187,9 +215,12 @@ async def create_event(
 
     data = event.model_dump()
 
-    # Resolve calendar_id to default if not provided
+    # Resolve calendar_id to user's default if not provided
     if not data.get("calendar_id"):
-        data["calendar_id"] = await _get_default_calendar_id(db)
+        data["calendar_id"] = await _get_default_calendar_id(db, current_user.id)
+    else:
+        # SEC-04: verify the target calendar belongs to the requesting user
+        await _verify_calendar_ownership(db, data["calendar_id"], current_user.id)
 
     # Serialize RecurrenceRule object to JSON string for DB storage
     # Exclude None values so defaults in recurrence service work correctly
@@ -245,10 +276,15 @@ async def get_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+
     result = await db.execute(
         select(CalendarEvent)
         .options(selectinload(CalendarEvent.calendar))
-        .where(CalendarEvent.id == event_id)
+        .where(
+            CalendarEvent.id == event_id,
+            CalendarEvent.calendar_id.in_(user_calendar_ids),
+        )
     )
     event = result.scalar_one_or_none()
 
@@ -265,10 +301,15 @@ async def update_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+
     result = await db.execute(
         select(CalendarEvent)
         .options(selectinload(CalendarEvent.calendar))
-        .where(CalendarEvent.id == event_id)
+        .where(
+            CalendarEvent.id == event_id,
+            CalendarEvent.calendar_id.in_(user_calendar_ids),
+        )
     )
     event = result.scalar_one_or_none()
 
@@ -285,6 +326,10 @@ async def update_event(
     if rule_obj is not None:
         update_data["recurrence_rule"] = json.dumps({k: v for k, v in rule_obj.items() if v is not None}) if rule_obj else None
 
+    # SEC-04: if calendar_id is being changed, verify the target belongs to the user
+    if "calendar_id" in update_data and update_data["calendar_id"] is not None:
+        await _verify_calendar_ownership(db, update_data["calendar_id"], current_user.id)
+
     start = update_data.get("start_datetime", event.start_datetime)
     end_dt = update_data.get("end_datetime", event.end_datetime)
     if end_dt is not None and end_dt < start:
@@ -381,7 +426,14 @@ async def delete_event(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    result = await db.execute(select(CalendarEvent).where(CalendarEvent.id == event_id))
+    user_calendar_ids = select(Calendar.id).where(Calendar.user_id == current_user.id)
+
+    result = await db.execute(
+        select(CalendarEvent).where(
+            CalendarEvent.id == event_id,
+            CalendarEvent.calendar_id.in_(user_calendar_ids),
+        )
+    )
     event = result.scalar_one_or_none()
 
     if not event:
diff --git a/backend/app/routers/locations.py b/backend/app/routers/locations.py
index ed64541..e209d8f 100644
--- a/backend/app/routers/locations.py
+++ b/backend/app/routers/locations.py
@@ -29,14 +29,15 @@ async def search_locations(
     """Search locations from local DB and Nominatim OSM."""
     results: List[LocationSearchResult] = []
 
-    # Local DB search
+    # Local DB search — scoped to user's locations
     local_query = (
         select(Location)
         .where(
+            Location.user_id == current_user.id,
             or_(
                 Location.name.ilike(f"%{q}%"),
                 Location.address.ilike(f"%{q}%"),
-            )
+            ),
         )
         .limit(5)
     )
@@ -89,7 +90,7 @@ async def get_locations(
     current_user: User = Depends(get_current_user)
 ):
     """Get all locations with optional category filter."""
-    query = select(Location)
+    query = select(Location).where(Location.user_id == current_user.id)
 
     if category:
         query = query.where(Location.category == category)
@@ -109,7 +110,7 @@ async def create_location(
     current_user: User = Depends(get_current_user)
 ):
     """Create a new location."""
-    new_location = Location(**location.model_dump())
+    new_location = Location(**location.model_dump(), user_id=current_user.id)
     db.add(new_location)
     await db.commit()
     await db.refresh(new_location)
@@ -124,7 +125,9 @@ async def get_location(
     current_user: User = Depends(get_current_user)
 ):
     """Get a specific location by ID."""
-    result = await db.execute(select(Location).where(Location.id == location_id))
+    result = await db.execute(
+        select(Location).where(Location.id == location_id, Location.user_id == current_user.id)
+    )
     location = result.scalar_one_or_none()
 
     if not location:
@@ -141,7 +144,9 @@ async def update_location(
     current_user: User = Depends(get_current_user)
 ):
     """Update a location."""
-    result = await db.execute(select(Location).where(Location.id == location_id))
+    result = await db.execute(
+        select(Location).where(Location.id == location_id, Location.user_id == current_user.id)
+    )
     location = result.scalar_one_or_none()
 
     if not location:
@@ -168,7 +173,9 @@ async def delete_location(
     current_user: User = Depends(get_current_user)
 ):
     """Delete a location."""
-    result = await db.execute(select(Location).where(Location.id == location_id))
+    result = await db.execute(
+        select(Location).where(Location.id == location_id, Location.user_id == current_user.id)
+    )
     location = result.scalar_one_or_none()
 
     if not location:
diff --git a/backend/app/routers/people.py b/backend/app/routers/people.py
index 150f268..2bee2b1 100644
--- a/backend/app/routers/people.py
+++ b/backend/app/routers/people.py
@@ -37,7 +37,7 @@ async def get_people(
     current_user: User = Depends(get_current_user)
 ):
     """Get all people with optional search and category filter."""
-    query = select(Person)
+    query = select(Person).where(Person.user_id == current_user.id)
 
     if search:
         term = f"%{search}%"
@@ -75,7 +75,7 @@ async def create_person(
         parts = data['name'].split(' ', 1)
         data['first_name'] = parts[0]
         data['last_name'] = parts[1] if len(parts) > 1 else None
-    new_person = Person(**data)
+    new_person = Person(**data, user_id=current_user.id)
     new_person.name = _compute_display_name(
         new_person.first_name,
         new_person.last_name,
@@ -96,7 +96,9 @@ async def get_person(
     current_user: User = Depends(get_current_user)
 ):
     """Get a specific person by ID."""
-    result = await db.execute(select(Person).where(Person.id == person_id))
+    result = await db.execute(
+        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
+    )
     person = result.scalar_one_or_none()
 
     if not person:
@@ -113,7 +115,9 @@ async def update_person(
     current_user: User = Depends(get_current_user)
 ):
     """Update a person and refresh the denormalised display name."""
-    result = await db.execute(select(Person).where(Person.id == person_id))
+    result = await db.execute(
+        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
+    )
     person = result.scalar_one_or_none()
 
     if not person:
@@ -147,7 +151,9 @@ async def delete_person(
     current_user: User = Depends(get_current_user)
 ):
     """Delete a person."""
-    result = await db.execute(select(Person).where(Person.id == person_id))
+    result = await db.execute(
+        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
+    )
     person = result.scalar_one_or_none()
 
     if not person:
diff --git a/backend/app/routers/projects.py b/backend/app/routers/projects.py
index dd86618..c49fecf 100644
--- a/backend/app/routers/projects.py
+++ b/backend/app/routers/projects.py
@@ -49,7 +49,12 @@ async def get_projects(
     current_user: User = Depends(get_current_user)
 ):
     """Get all projects with their tasks. Optionally filter by tracked status."""
-    query = select(Project).options(*_project_load_options()).order_by(Project.created_at.desc())
+    query = (
+        select(Project)
+        .options(*_project_load_options())
+        .where(Project.user_id == current_user.id)
+        .order_by(Project.created_at.desc())
+    )
     if tracked is not None:
         query = query.where(Project.is_tracked == tracked)
     result = await db.execute(query)
@@ -77,6 +82,7 @@ async def get_tracked_tasks(
             selectinload(ProjectTask.parent_task),
         )
         .where(
+            Project.user_id == current_user.id,
             Project.is_tracked == True,
             ProjectTask.due_date.isnot(None),
             ProjectTask.due_date >= today,
@@ -110,7 +116,7 @@ async def create_project(
     current_user: User = Depends(get_current_user)
 ):
     """Create a new project."""
-    new_project = Project(**project.model_dump())
+    new_project = Project(**project.model_dump(), user_id=current_user.id)
     db.add(new_project)
     await db.commit()
 
@@ -127,7 +133,11 @@ async def get_project(
     current_user: User = Depends(get_current_user)
 ):
     """Get a specific project by ID with its tasks."""
-    query = select(Project).options(*_project_load_options()).where(Project.id == project_id)
+    query = (
+        select(Project)
+        .options(*_project_load_options())
+        .where(Project.id == project_id, Project.user_id == current_user.id)
+    )
     result = await db.execute(query)
     project = result.scalar_one_or_none()
 
@@ -145,7 +155,9 @@ async def update_project(
     current_user: User = Depends(get_current_user)
 ):
     """Update a project."""
-    result = await db.execute(select(Project).where(Project.id == project_id))
+    result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
     project = result.scalar_one_or_none()
 
     if not project:
@@ -171,7 +183,9 @@ async def delete_project(
     current_user: User = Depends(get_current_user)
 ):
     """Delete a project and all its tasks."""
-    result = await db.execute(select(Project).where(Project.id == project_id))
+    result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
     project = result.scalar_one_or_none()
 
     if not project:
@@ -190,7 +204,10 @@ async def get_project_tasks(
     current_user: User = Depends(get_current_user)
 ):
     """Get top-level tasks for a specific project (subtasks are nested)."""
-    result = await db.execute(select(Project).where(Project.id == project_id))
+    # Verify project ownership first
+    result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
     project = result.scalar_one_or_none()
 
     if not project:
@@ -219,7 +236,10 @@ async def create_project_task(
     current_user: User = Depends(get_current_user)
 ):
     """Create a new task or subtask for a project."""
-    result = await db.execute(select(Project).where(Project.id == project_id))
+    # Verify project ownership first
+    result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
     project = result.scalar_one_or_none()
 
     if not project:
@@ -265,7 +285,10 @@ async def reorder_tasks(
     current_user: User = Depends(get_current_user)
 ):
     """Bulk update sort_order for tasks."""
-    result = await db.execute(select(Project).where(Project.id == project_id))
+    # Verify project ownership first
+    result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
     project = result.scalar_one_or_none()
 
     if not project:
@@ -296,6 +319,13 @@ async def update_project_task(
     current_user: User = Depends(get_current_user)
 ):
     """Update a project task."""
+    # Verify project ownership first, then fetch task scoped to that project
+    project_result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
+    if not project_result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Project not found")
+
     result = await db.execute(
         select(ProjectTask).where(
             ProjectTask.id == task_id,
@@ -332,6 +362,13 @@ async def delete_project_task(
     current_user: User = Depends(get_current_user)
 ):
     """Delete a project task (cascades to subtasks)."""
+    # Verify project ownership first, then fetch task scoped to that project
+    project_result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
+    if not project_result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Project not found")
+
     result = await db.execute(
         select(ProjectTask).where(
             ProjectTask.id == task_id,
@@ -358,6 +395,13 @@ async def create_task_comment(
     current_user: User = Depends(get_current_user)
 ):
     """Add a comment to a task."""
+    # Verify project ownership first, then fetch task scoped to that project
+    project_result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
+    if not project_result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Project not found")
+
     result = await db.execute(
         select(ProjectTask).where(
             ProjectTask.id == task_id,
@@ -386,6 +430,13 @@ async def delete_task_comment(
     current_user: User = Depends(get_current_user)
 ):
     """Delete a task comment."""
+    # Verify project ownership first, then fetch comment scoped through task
+    project_result = await db.execute(
+        select(Project).where(Project.id == project_id, Project.user_id == current_user.id)
+    )
+    if not project_result.scalar_one_or_none():
+        raise HTTPException(status_code=404, detail="Project not found")
+
     result = await db.execute(
         select(TaskComment).where(
             TaskComment.id == comment_id,
diff --git a/backend/app/routers/reminders.py b/backend/app/routers/reminders.py
index b33872a..788ea79 100644
--- a/backend/app/routers/reminders.py
+++ b/backend/app/routers/reminders.py
@@ -22,7 +22,7 @@ async def get_reminders(
     current_user: User = Depends(get_current_user)
 ):
     """Get all reminders with optional filters."""
-    query = select(Reminder)
+    query = select(Reminder).where(Reminder.user_id == current_user.id)
 
     if active is not None:
         query = query.where(Reminder.is_active == active)
@@ -48,6 +48,7 @@ async def get_due_reminders(
     now = client_now or datetime.now()
     query = select(Reminder).where(
         and_(
+            Reminder.user_id == current_user.id,
             Reminder.remind_at <= now,
             Reminder.is_dismissed == False,
             Reminder.is_active == True,
@@ -74,7 +75,12 @@ async def snooze_reminder(
     current_user: User = Depends(get_current_user)
 ):
     """Snooze a reminder for N minutes from now."""
-    result = await db.execute(select(Reminder).where(Reminder.id == reminder_id))
+    result = await db.execute(
+        select(Reminder).where(
+            Reminder.id == reminder_id,
+            Reminder.user_id == current_user.id,
+        )
+    )
     reminder = result.scalar_one_or_none()
 
     if not reminder:
@@ -99,7 +105,7 @@ async def create_reminder(
     current_user: User = Depends(get_current_user)
 ):
     """Create a new reminder."""
-    new_reminder = Reminder(**reminder.model_dump())
+    new_reminder = Reminder(**reminder.model_dump(), user_id=current_user.id)
     db.add(new_reminder)
     await db.commit()
     await db.refresh(new_reminder)
@@ -114,7 +120,12 @@ async def get_reminder(
     current_user: User = Depends(get_current_user)
 ):
     """Get a specific reminder by ID."""
-    result = await db.execute(select(Reminder).where(Reminder.id == reminder_id))
+    result = await db.execute(
+        select(Reminder).where(
+            Reminder.id == reminder_id,
+            Reminder.user_id == current_user.id,
+        )
+    )
     reminder = result.scalar_one_or_none()
 
     if not reminder:
@@ -131,7 +142,12 @@ async def update_reminder(
     current_user: User = Depends(get_current_user)
 ):
     """Update a reminder."""
-    result = await db.execute(select(Reminder).where(Reminder.id == reminder_id))
+    result = await db.execute(
+        select(Reminder).where(
+            Reminder.id == reminder_id,
+            Reminder.user_id == current_user.id,
+        )
+    )
     reminder = result.scalar_one_or_none()
 
     if not reminder:
@@ -164,7 +180,12 @@ async def delete_reminder(
     current_user: User = Depends(get_current_user)
 ):
     """Delete a reminder."""
-    result = await db.execute(select(Reminder).where(Reminder.id == reminder_id))
+    result = await db.execute(
+        select(Reminder).where(
+            Reminder.id == reminder_id,
+            Reminder.user_id == current_user.id,
+        )
+    )
     reminder = result.scalar_one_or_none()
 
     if not reminder:
@@ -183,7 +204,12 @@ async def dismiss_reminder(
     current_user: User = Depends(get_current_user)
 ):
     """Dismiss a reminder."""
-    result = await db.execute(select(Reminder).where(Reminder.id == reminder_id))
+    result = await db.execute(
+        select(Reminder).where(
+            Reminder.id == reminder_id,
+            Reminder.user_id == current_user.id,
+        )
+    )
     reminder = result.scalar_one_or_none()
 
     if not reminder:
diff --git a/backend/app/routers/todos.py b/backend/app/routers/todos.py
index 57841a7..86cdf65 100644
--- a/backend/app/routers/todos.py
+++ b/backend/app/routers/todos.py
@@ -73,15 +73,17 @@ def _calculate_recurrence(
     return reset_at, next_due
 
 
-async def _reactivate_recurring_todos(db: AsyncSession) -> None:
+async def _reactivate_recurring_todos(db: AsyncSession, user_id: int) -> None:
     """Auto-reactivate recurring todos whose reset_at has passed.
 
     Uses flush (not commit) so changes are visible to the subsequent query
     within the same transaction. The caller's commit handles persistence.
+    Scoped to a single user to avoid cross-user reactivation.
     """
     now = datetime.now()
     query = select(Todo).where(
         and_(
+            Todo.user_id == user_id,
             Todo.completed == True,
             Todo.recurrence_rule.isnot(None),
             Todo.reset_at.isnot(None),
@@ -110,13 +112,14 @@ async def get_todos(
     category: Optional[str] = Query(None),
     search: Optional[str] = Query(None),
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
+    current_settings: Settings = Depends(get_current_settings),
 ):
     """Get all todos with optional filters."""
     # Reactivate any recurring todos whose reset time has passed
-    await _reactivate_recurring_todos(db)
+    await _reactivate_recurring_todos(db, current_user.id)
 
-    query = select(Todo)
+    query = select(Todo).where(Todo.user_id == current_user.id)
 
     if completed is not None:
         query = query.where(Todo.completed == completed)
@@ -144,10 +147,10 @@ async def get_todos(
 async def create_todo(
     todo: TodoCreate,
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
 ):
     """Create a new todo."""
-    new_todo = Todo(**todo.model_dump())
+    new_todo = Todo(**todo.model_dump(), user_id=current_user.id)
     db.add(new_todo)
     await db.commit()
     await db.refresh(new_todo)
@@ -159,10 +162,12 @@ async def create_todo(
 async def get_todo(
     todo_id: int,
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
 ):
     """Get a specific todo by ID."""
-    result = await db.execute(select(Todo).where(Todo.id == todo_id))
+    result = await db.execute(
+        select(Todo).where(Todo.id == todo_id, Todo.user_id == current_user.id)
+    )
     todo = result.scalar_one_or_none()
 
     if not todo:
@@ -176,10 +181,13 @@ async def update_todo(
     todo_id: int,
     todo_update: TodoUpdate,
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
+    current_settings: Settings = Depends(get_current_settings),
 ):
     """Update a todo."""
-    result = await db.execute(select(Todo).where(Todo.id == todo_id))
+    result = await db.execute(
+        select(Todo).where(Todo.id == todo_id, Todo.user_id == current_user.id)
+    )
     todo = result.scalar_one_or_none()
 
     if not todo:
@@ -210,7 +218,7 @@ async def update_todo(
         reset_at, next_due = _calculate_recurrence(
             todo.recurrence_rule,
             todo.due_date,
-            current_user.first_day_of_week,
+            current_settings.first_day_of_week,
         )
         todo.reset_at = reset_at
         todo.next_due_date = next_due
@@ -229,10 +237,12 @@ async def update_todo(
 async def delete_todo(
     todo_id: int,
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
 ):
     """Delete a todo."""
-    result = await db.execute(select(Todo).where(Todo.id == todo_id))
+    result = await db.execute(
+        select(Todo).where(Todo.id == todo_id, Todo.user_id == current_user.id)
+    )
     todo = result.scalar_one_or_none()
 
     if not todo:
@@ -248,10 +258,13 @@ async def delete_todo(
 async def toggle_todo(
     todo_id: int,
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
+    current_settings: Settings = Depends(get_current_settings),
 ):
     """Toggle todo completion status. For recurring todos, calculates reset schedule."""
-    result = await db.execute(select(Todo).where(Todo.id == todo_id))
+    result = await db.execute(
+        select(Todo).where(Todo.id == todo_id, Todo.user_id == current_user.id)
+    )
     todo = result.scalar_one_or_none()
 
     if not todo:
@@ -267,7 +280,7 @@ async def toggle_todo(
             reset_at, next_due = _calculate_recurrence(
                 todo.recurrence_rule,
                 todo.due_date,
-                current_user.first_day_of_week,
+                current_settings.first_day_of_week,
             )
             todo.reset_at = reset_at
             todo.next_due_date = next_due
diff --git a/backend/app/routers/weather.py b/backend/app/routers/weather.py
index 25f8b94..bed8724 100644
--- a/backend/app/routers/weather.py
+++ b/backend/app/routers/weather.py
@@ -3,6 +3,7 @@ from pydantic import BaseModel
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
 from datetime import datetime, timedelta
+from collections import OrderedDict
 import asyncio
 import urllib.request
 import urllib.parse
@@ -11,13 +12,37 @@ import json
 
 from app.database import get_db
 from app.models.settings import Settings
+from app.models.user import User
 from app.config import settings as app_settings
 from app.routers.auth import get_current_user, get_current_settings
-from app.models.user import User
 
 router = APIRouter()
 
-_cache: dict = {}
+# SEC-15: Bounded LRU cache keyed by (user_id, location) — max 100 entries.
+# OrderedDict preserves insertion order; move_to_end on hit, popitem(last=False)
+# to evict the oldest when capacity is exceeded.
+_CACHE_MAX = 100
+_cache: OrderedDict = OrderedDict()
+
+
+def _cache_get(key: tuple) -> dict | None:
+    """Return cached entry if it exists and hasn't expired."""
+    entry = _cache.get(key)
+    if entry and datetime.now() < entry["expires_at"]:
+        _cache.move_to_end(key)  # LRU: promote to most-recently-used
+        return entry["data"]
+    if entry:
+        del _cache[key]  # expired — evict immediately
+    return None
+
+
+def _cache_set(key: tuple, data: dict) -> None:
+    """Store an entry; evict the oldest if over capacity."""
+    if key in _cache:
+        _cache.move_to_end(key)
+    _cache[key] = {"data": data, "expires_at": datetime.now() + timedelta(hours=1)}
+    while len(_cache) > _CACHE_MAX:
+        _cache.popitem(last=False)  # evict LRU (oldest)
 
 
 class GeoSearchResult(BaseModel):
@@ -66,23 +91,24 @@ async def search_locations(
 @router.get("/")
 async def get_weather(
     db: AsyncSession = Depends(get_db),
-    current_user: Settings = Depends(get_current_settings)
+    current_user: User = Depends(get_current_user),
+    current_settings: Settings = Depends(get_current_settings),
 ):
-    city = current_user.weather_city
-    lat = current_user.weather_lat
-    lon = current_user.weather_lon
+    city = current_settings.weather_city
+    lat = current_settings.weather_lat
+    lon = current_settings.weather_lon
 
     if not city and (lat is None or lon is None):
         raise HTTPException(status_code=400, detail="No weather location configured")
 
-    # Build cache key from coordinates or city
+    # Cache key includes user_id so each user gets isolated cache entries
     use_coords = lat is not None and lon is not None
-    cache_key = f"{lat},{lon}" if use_coords else city
+    location_key = f"{lat},{lon}" if use_coords else city
+    cache_key = (current_user.id, location_key)
 
-    # Check cache
-    now = datetime.now()
-    if _cache.get("expires_at") and now < _cache["expires_at"] and _cache.get("cache_key") == cache_key:
-        return _cache["data"]
+    cached = _cache_get(cache_key)
+    if cached is not None:
+        return cached
 
     api_key = app_settings.OPENWEATHERMAP_API_KEY
     if not api_key:
@@ -122,11 +148,7 @@ async def get_weather(
             "city": current_data["name"],
         }
 
-        # Cache for 1 hour
-        _cache["data"] = weather_result
-        _cache["expires_at"] = now + timedelta(hours=1)
-        _cache["cache_key"] = cache_key
-
+        _cache_set(cache_key, weather_result)
         return weather_result
 
     except urllib.error.URLError:
diff --git a/backend/app/schemas/admin.py b/backend/app/schemas/admin.py
new file mode 100644
index 0000000..075a916
--- /dev/null
+++ b/backend/app/schemas/admin.py
@@ -0,0 +1,133 @@
+"""
+Admin API schemas — Pydantic v2.
+
+All admin-facing request/response shapes live here to keep the admin router
+clean and testable in isolation.
+"""
+import re
+from datetime import datetime
+from typing import Optional, Literal
+
+from pydantic import BaseModel, ConfigDict, field_validator
+
+from app.schemas.auth import _validate_username, _validate_password_strength
+
+
+# ---------------------------------------------------------------------------
+# User list / detail
+# ---------------------------------------------------------------------------
+
+class UserListItem(BaseModel):
+    id: int
+    username: str
+    role: str
+    is_active: bool
+    last_login_at: Optional[datetime] = None
+    last_password_change_at: Optional[datetime] = None
+    totp_enabled: bool
+    mfa_enforce_pending: bool
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class UserListResponse(BaseModel):
+    users: list[UserListItem]
+    total: int
+
+
+class UserDetailResponse(UserListItem):
+    active_sessions: int
+
+
+# ---------------------------------------------------------------------------
+# Mutating user requests
+# ---------------------------------------------------------------------------
+
+class CreateUserRequest(BaseModel):
+    """Admin-created user — allows role selection (unlike public RegisterRequest)."""
+    model_config = ConfigDict(extra="forbid")
+
+    username: str
+    password: str
+    role: Literal["admin", "standard", "public_event_manager"] = "standard"
+
+    @field_validator("username")
+    @classmethod
+    def validate_username(cls, v: str) -> str:
+        return _validate_username(v)
+
+    @field_validator("password")
+    @classmethod
+    def validate_password(cls, v: str) -> str:
+        return _validate_password_strength(v)
+
+
+class UpdateUserRoleRequest(BaseModel):
+    role: Literal["admin", "standard", "public_event_manager"]
+
+
+class ToggleActiveRequest(BaseModel):
+    is_active: bool
+
+
+class ToggleMfaEnforceRequest(BaseModel):
+    enforce: bool
+
+
+# ---------------------------------------------------------------------------
+# System config
+# ---------------------------------------------------------------------------
+
+class SystemConfigResponse(BaseModel):
+    allow_registration: bool
+    enforce_mfa_new_users: bool
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class SystemConfigUpdate(BaseModel):
+    allow_registration: Optional[bool] = None
+    enforce_mfa_new_users: Optional[bool] = None
+
+
+# ---------------------------------------------------------------------------
+# Admin dashboard
+# ---------------------------------------------------------------------------
+
+class AdminDashboardResponse(BaseModel):
+    total_users: int
+    active_users: int
+    admin_count: int
+    active_sessions: int
+    mfa_adoption_rate: float
+    recent_logins: list[dict]
+    recent_audit_entries: list[dict]
+
+
+# ---------------------------------------------------------------------------
+# Password reset
+# ---------------------------------------------------------------------------
+
+class ResetPasswordResponse(BaseModel):
+    message: str
+    temporary_password: str
+
+
+# ---------------------------------------------------------------------------
+# Audit log
+# ---------------------------------------------------------------------------
+
+class AuditLogEntry(BaseModel):
+    id: int
+    actor_username: Optional[str] = None
+    target_username: Optional[str] = None
+    action: str
+    detail: Optional[str] = None
+    ip_address: Optional[str] = None
+    created_at: datetime
+
+
+class AuditLogResponse(BaseModel):
+    entries: list[AuditLogEntry]
+    total: int
diff --git a/backend/app/schemas/auth.py b/backend/app/schemas/auth.py
index 806835d..a45dba3 100644
--- a/backend/app/schemas/auth.py
+++ b/backend/app/schemas/auth.py
@@ -1,5 +1,5 @@
 import re
-from pydantic import BaseModel, field_validator
+from pydantic import BaseModel, ConfigDict, field_validator
 
 
 def _validate_password_strength(v: str) -> str:
@@ -21,6 +21,16 @@ def _validate_password_strength(v: str) -> str:
     return v
 
 
+def _validate_username(v: str) -> str:
+    """Shared username validation."""
+    v = v.strip().lower()
+    if not 3 <= len(v) <= 50:
+        raise ValueError("Username must be 3–50 characters")
+    if not re.fullmatch(r"[a-z0-9_\-]+", v):
+        raise ValueError("Username may only contain letters, numbers, _ and -")
+    return v
+
+
 class SetupRequest(BaseModel):
     username: str
     password: str
@@ -28,12 +38,29 @@ class SetupRequest(BaseModel):
     @field_validator("username")
     @classmethod
     def validate_username(cls, v: str) -> str:
-        v = v.strip().lower()
-        if not 3 <= len(v) <= 50:
-            raise ValueError("Username must be 3–50 characters")
-        if not re.fullmatch(r"[a-z0-9_\-]+", v):
-            raise ValueError("Username may only contain letters, numbers, _ and -")
-        return v
+        return _validate_username(v)
+
+    @field_validator("password")
+    @classmethod
+    def validate_password(cls, v: str) -> str:
+        return _validate_password_strength(v)
+
+
+class RegisterRequest(BaseModel):
+    """
+    Public registration schema — SEC-01: extra="forbid" prevents role injection.
+    An attacker sending {"username": "...", "password": "...", "role": "admin"}
+    will get a 422 Validation Error instead of silent acceptance.
+    """
+    model_config = ConfigDict(extra="forbid")
+
+    username: str
+    password: str
+
+    @field_validator("username")
+    @classmethod
+    def validate_username(cls, v: str) -> str:
+        return _validate_username(v)
 
     @field_validator("password")
     @classmethod
diff --git a/backend/app/services/audit.py b/backend/app/services/audit.py
new file mode 100644
index 0000000..a38548c
--- /dev/null
+++ b/backend/app/services/audit.py
@@ -0,0 +1,22 @@
+import json
+from sqlalchemy.ext.asyncio import AsyncSession
+from app.models.audit_log import AuditLog
+
+
+async def log_audit_event(
+    db: AsyncSession,
+    action: str,
+    actor_id: int | None = None,
+    target_id: int | None = None,
+    detail: dict | None = None,
+    ip: str | None = None,
+) -> None:
+    """Record an action in the audit log. Does NOT commit — caller handles transaction."""
+    entry = AuditLog(
+        actor_user_id=actor_id,
+        target_user_id=target_id,
+        action=action,
+        detail=json.dumps(detail) if detail else None,
+        ip_address=ip[:45] if ip else None,
+    )
+    db.add(entry)
diff --git a/backend/app/services/auth.py b/backend/app/services/auth.py
index 186524b..adf2323 100644
--- a/backend/app/services/auth.py
+++ b/backend/app/services/auth.py
@@ -126,3 +126,32 @@ def verify_mfa_token(token: str) -> int | None:
         return data["uid"]
     except Exception:
         return None
+
+
+# ---------------------------------------------------------------------------
+# MFA enforcement tokens (SEC-03: distinct salt from challenge tokens)
+# ---------------------------------------------------------------------------
+
+_mfa_enforce_serializer = URLSafeTimedSerializer(
+    secret_key=app_settings.SECRET_KEY,
+    salt="mfa-enforce-setup-v1",
+)
+
+
+def create_mfa_enforce_token(user_id: int) -> str:
+    """Create a short-lived token for MFA enforcement setup (not a session)."""
+    return _mfa_enforce_serializer.dumps({"uid": user_id})
+
+
+def verify_mfa_enforce_token(token: str) -> int | None:
+    """
+    Verify an MFA enforcement setup token.
+    Returns user_id on success, None if invalid or expired (5-minute TTL).
+    """
+    try:
+        data = _mfa_enforce_serializer.loads(
+            token, max_age=app_settings.MFA_TOKEN_MAX_AGE_SECONDS
+        )
+        return data["uid"]
+    except Exception:
+        return None
diff --git a/frontend/nginx.conf b/frontend/nginx.conf
index 3519178..1e8bbd8 100644
--- a/frontend/nginx.conf
+++ b/frontend/nginx.conf
@@ -1,5 +1,9 @@
 # Rate limiting zones (before server block)
 limit_req_zone $binary_remote_addr zone=auth_limit:10m rate=10r/m;
+# SEC-14: Registration endpoint — slightly more permissive than strict auth endpoints
+limit_req_zone $binary_remote_addr zone=register_limit:10m rate=5r/m;
+# Admin API — generous for legitimate use but still guards against scraping/brute-force
+limit_req_zone $binary_remote_addr zone=admin_limit:10m rate=30r/m;
 
 # Use X-Forwarded-Proto from upstream proxy when present, fall back to $scheme for direct access
 map $http_x_forwarded_proto $forwarded_proto {
@@ -60,6 +64,20 @@ server {
         include /etc/nginx/proxy-params.conf;
     }
 
+    # SEC-14: Rate-limit public registration endpoint
+    location /api/auth/register {
+        limit_req zone=register_limit burst=3 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
+    # Admin API — rate-limited separately from general /api traffic
+    location /api/admin/ {
+        limit_req zone=admin_limit burst=10 nodelay;
+        limit_req_status 429;
+        include /etc/nginx/proxy-params.conf;
+    }
+
     # API proxy
     location /api {
         proxy_pass http://backend:8000;
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 6e1694d..a969411 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -1,3 +1,4 @@
+import { lazy, Suspense } from 'react';
 import { Routes, Route, Navigate } from 'react-router-dom';
 import { useAuth } from '@/hooks/useAuth';
 import LockScreen from '@/components/auth/LockScreen';
@@ -12,6 +13,8 @@ import PeoplePage from '@/components/people/PeoplePage';
 import LocationsPage from '@/components/locations/LocationsPage';
 import SettingsPage from '@/components/settings/SettingsPage';
 
+const AdminPortal = lazy(() => import('@/components/admin/AdminPortal'));
+
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
   const { authStatus, isLoading } = useAuth();
 
@@ -30,6 +33,24 @@ function ProtectedRoute({ children }: { children: React.ReactNode }) {
   return <>{children}</>;
 }
 
+function AdminRoute({ children }: { children: React.ReactNode }) {
+  const { authStatus, isLoading } = useAuth();
+
+  if (isLoading) {
+    return (
+      <div className="flex h-screen items-center justify-center">
+        <div className="text-muted-foreground">Loading...</div>
+      </div>
+    );
+  }
+
+  if (!authStatus?.authenticated || authStatus?.role !== 'admin') {
+    return <Navigate to="/dashboard" replace />;
+  }
+
+  return <>{children}</>;
+}
+
 function App() {
   return (
     <Routes>
@@ -52,6 +73,16 @@ function App() {
         <Route path="people" element={<PeoplePage />} />
         <Route path="locations" element={<LocationsPage />} />
         <Route path="settings" element={<SettingsPage />} />
+        <Route
+          path="admin/*"
+          element={
+            <AdminRoute>
+              <Suspense fallback={<div className="flex h-full items-center justify-center text-muted-foreground">Loading...</div>}>
+                <AdminPortal />
+              </Suspense>
+            </AdminRoute>
+          }
+        />
       </Route>
     </Routes>
   );
diff --git a/frontend/src/components/layout/Sidebar.tsx b/frontend/src/components/layout/Sidebar.tsx
index e269f9e..78ea3ed 100644
--- a/frontend/src/components/layout/Sidebar.tsx
+++ b/frontend/src/components/layout/Sidebar.tsx
@@ -16,6 +16,7 @@ import {
   X,
   LogOut,
   Lock,
+  Shield,
 } from 'lucide-react';
 import { cn } from '@/lib/utils';
 import { useAuth } from '@/hooks/useAuth';
@@ -44,7 +45,7 @@ interface SidebarProps {
 export default function Sidebar({ collapsed, onToggle, mobileOpen, onMobileClose }: SidebarProps) {
   const navigate = useNavigate();
   const location = useLocation();
-  const { logout } = useAuth();
+  const { logout, isAdmin } = useAuth();
   const { lock } = useLock();
   const [projectsExpanded, setProjectsExpanded] = useState(false);
 
@@ -193,6 +194,16 @@ export default function Sidebar({ collapsed, onToggle, mobileOpen, onMobileClose
           <Lock className="h-5 w-5 shrink-0" />
           {showExpanded && <span>Lock</span>}
         </button>
+        {isAdmin && (
+          <NavLink
+            to="/admin"
+            onClick={mobileOpen ? onMobileClose : undefined}
+            className={navLinkClass}
+          >
+            <Shield className="h-5 w-5 shrink-0" />
+            {showExpanded && <span>Admin</span>}
+          </NavLink>
+        )}
         <NavLink
           to="/settings"
           onClick={mobileOpen ? onMobileClose : undefined}
diff --git a/frontend/src/hooks/useAuth.ts b/frontend/src/hooks/useAuth.ts
index e31ad48..239fe2f 100644
--- a/frontend/src/hooks/useAuth.ts
+++ b/frontend/src/hooks/useAuth.ts
@@ -5,8 +5,8 @@ import type { AuthStatus, LoginResponse } from '@/types';
 
 export function useAuth() {
   const queryClient = useQueryClient();
-  // Ephemeral MFA token — not in TanStack cache, lives only during the TOTP challenge step
   const [mfaToken, setMfaToken] = useState<string | null>(null);
+  const [mfaSetupRequired, setMfaSetupRequired] = useState(false);
 
   const authQuery = useQuery({
     queryKey: ['auth'],
@@ -23,11 +23,34 @@ export function useAuth() {
       return data;
     },
     onSuccess: (data) => {
-      if ('mfa_token' in data && data.totp_required) {
-        // MFA required — store token locally, do NOT mark as authenticated yet
+      if ('mfa_setup_required' in data && data.mfa_setup_required) {
+        // MFA enforcement — user must set up TOTP before accessing app
+        setMfaSetupRequired(true);
+        setMfaToken(data.mfa_token);
+      } else if ('mfa_token' in data && 'totp_required' in data && data.totp_required) {
+        // Regular TOTP challenge
+        setMfaToken(data.mfa_token);
+        setMfaSetupRequired(false);
+      } else {
+        setMfaToken(null);
+        setMfaSetupRequired(false);
+        queryClient.invalidateQueries({ queryKey: ['auth'] });
+      }
+    },
+  });
+
+  const registerMutation = useMutation({
+    mutationFn: async ({ username, password }: { username: string; password: string }) => {
+      const { data } = await api.post<LoginResponse & { message?: string }>('/auth/register', { username, password });
+      return data;
+    },
+    onSuccess: (data) => {
+      if ('mfa_setup_required' in data && data.mfa_setup_required) {
+        setMfaSetupRequired(true);
         setMfaToken(data.mfa_token);
       } else {
         setMfaToken(null);
+        setMfaSetupRequired(false);
         queryClient.invalidateQueries({ queryKey: ['auth'] });
       }
     },
@@ -43,6 +66,7 @@ export function useAuth() {
     },
     onSuccess: () => {
       setMfaToken(null);
+      setMfaSetupRequired(false);
       queryClient.invalidateQueries({ queryKey: ['auth'] });
     },
   });
@@ -64,6 +88,7 @@ export function useAuth() {
     },
     onSuccess: () => {
       setMfaToken(null);
+      setMfaSetupRequired(false);
       queryClient.invalidateQueries({ queryKey: ['auth'] });
     },
   });
@@ -71,12 +96,18 @@ export function useAuth() {
   return {
     authStatus: authQuery.data,
     isLoading: authQuery.isLoading,
-    mfaRequired: mfaToken !== null,
+    role: authQuery.data?.role ?? null,
+    isAdmin: authQuery.data?.role === 'admin',
+    mfaRequired: mfaToken !== null && !mfaSetupRequired,
+    mfaSetupRequired,
+    mfaToken,
     login: loginMutation.mutateAsync,
+    register: registerMutation.mutateAsync,
     verifyTotp: totpVerifyMutation.mutateAsync,
     setup: setupMutation.mutateAsync,
     logout: logoutMutation.mutateAsync,
     isLoginPending: loginMutation.isPending,
+    isRegisterPending: registerMutation.isPending,
     isTotpPending: totpVerifyMutation.isPending,
     isSetupPending: setupMutation.isPending,
   };
diff --git a/frontend/src/lib/api.ts b/frontend/src/lib/api.ts
index 7913a72..c169e2d 100644
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@@ -4,6 +4,7 @@ const api = axios.create({
   baseURL: '/api',
   headers: {
     'Content-Type': 'application/json',
+    'X-Requested-With': 'XMLHttpRequest',
   },
   withCredentials: true,
 });
diff --git a/frontend/src/types/index.ts b/frontend/src/types/index.ts
index 510aacd..0cb34c4 100644
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -188,14 +188,19 @@ export interface Location {
   updated_at: string;
 }
 
+export type UserRole = 'admin' | 'standard' | 'public_event_manager';
+
 export interface AuthStatus {
   authenticated: boolean;
   setup_required: boolean;
+  role: UserRole | null;
+  registration_open: boolean;
 }
 
 // Login response discriminated union
 export interface LoginSuccessResponse {
   authenticated: true;
+  must_change_password?: boolean;
 }
 
 export interface LoginMfaRequiredResponse {
@@ -204,7 +209,64 @@ export interface LoginMfaRequiredResponse {
   mfa_token: string;
 }
 
-export type LoginResponse = LoginSuccessResponse | LoginMfaRequiredResponse;
+export interface LoginMfaSetupRequiredResponse {
+  authenticated: false;
+  mfa_setup_required: true;
+  mfa_token: string;
+}
+
+export type LoginResponse = LoginSuccessResponse | LoginMfaRequiredResponse | LoginMfaSetupRequiredResponse;
+
+// Admin types
+export interface AdminUser {
+  id: number;
+  username: string;
+  role: UserRole;
+  is_active: boolean;
+  last_login_at: string | null;
+  last_password_change_at: string | null;
+  totp_enabled: boolean;
+  mfa_enforce_pending: boolean;
+  created_at: string;
+}
+
+export interface AdminUserDetail extends AdminUser {
+  active_sessions: number;
+}
+
+export interface SystemConfig {
+  allow_registration: boolean;
+  enforce_mfa_new_users: boolean;
+}
+
+export interface AuditLogEntry {
+  id: number;
+  actor_username: string | null;
+  target_username: string | null;
+  action: string;
+  detail: string | null;
+  ip_address: string | null;
+  created_at: string;
+}
+
+export interface AdminDashboardData {
+  total_users: number;
+  active_users: number;
+  admin_count: number;
+  active_sessions: number;
+  mfa_adoption_rate: number;
+  recent_logins: Array<{
+    username: string;
+    last_login_at: string;
+    ip_address: string;
+  }>;
+  recent_audit_entries: Array<{
+    action: string;
+    actor_username: string | null;
+    target_username: string | null;
+    created_at: string;
+  }>;
+}
 
 // TOTP setup response (from POST /api/auth/totp/setup)
 export interface TotpSetupResponse {