CVE-2026-45399: Open WebUI: Low-privilege authenticated users can enumerate and stop global background tasks, causing system-wide chat disruption

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.