CVE-2026-45399

### Summary Any authenticated user with low privileges can enumerate active background tasks across the system and stop tasks belonging to other users via the GET /api/tasks and POST /api/tasks/stop/{task_id} methods. This allows a casual user to disrupt system-wide chat usage by continuously canceling other users' active tasks. This is a real authorization vulnerability affecting integrity and usability in multi-user deployments. ### Details Open WebUI exposes `GET /api/tasks` and `POST /api/tasks/stop/{task_id}` to any verified user. These endpoints operate on a global task namespace and accept raw `task_id` values without checking whether the task belongs to the current caller. As a result, a normal authenticated user can enumerate active global task IDs and stop tasks belonging to other users. Root cause: 1. Route authorization is too weak. In `backend/open_webui/main.py`, both endpoints only require `get_verified_user`: ```python @app.post('/api/tasks/stop/{task_id}') async def stop_task_endpoint(request: Request, task_id: str, user=Depends(get_verified_user)): result = await stop_task(request.app.state.redis, task_id) @app.get('/api/tasks') async def list_tasks_endpoint(request: Request, user=Depends(get_verified_user)): return {'tasks': await list_tasks(request.app.state.redis)} ``` `get_verified_user` accepts both `user` and `admin` roles in `backend/open_webui/utils/auth.py`. 2. The helper operates on a global namespace. In `backend/open_webui/tasks.py`, task listing is global: ```python async def list_tasks(redis): if redis: return await redis_list_tasks(redis) return list(tasks.keys()) ``` In `backend/open_webui/tasks.py`, task stopping is by raw `task_id`: ```python async def stop_task(redis, task_id: str): if redis: item_id = await redis.hget(REDIS_TASKS_KEY, task_id) await redis_send_command(redis, {'action': 'stop', 'task_id': task_id}) await redis_cleanup_task(redis, task_id, item_id o