CVE-2026-59225: Open WebUI: Arena task endpoints can bypass underlying model access controls

An authenticated non-admin user with read access to an arena wrapper model can reach a restricted underlying model through task endpoints such as /api/v1/tasks/moa/completions.

The normal chat route resolves arena models before the final chat dispatch and therefore re-checks the selected underlying model. The task routes call utils.chat.generate_chat_completion() directly. In that direct path, arena fallback resolution happens after the wrapper access check and then recurses with bypass_filter=True, skipping the selected submodel’s access check.