Open WebUI: Arena task endpoints can bypass underlying model access controls

Summary

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.

Technical Details

Open WebUI's current model-access behavior already denies direct access to the restricted model. The normal chat path also denies the selected restricted model after arena preprocessing. The task endpoint path is inconsistent with that protected behavior because it reaches the same restricted model only through the direct arena fallback and recursive bypass_filter=True.

This report does not rely on malicious provider configuration, user-authored Tools/Functions, or direct code execution. The crossed boundary is model read authorization.

Although the arena wrapper must be readable by the user, this is not just an "admin exposed a restricted model" configuration claim. The same configured arena is denied by the normal chat post-preprocessor control once the selected restricted model is the dispatch target. The bypass is specific to task endpoints that skip that preprocessor and enter the fallback arena resolver.

Official documentation also points to this interpretation:

• Open WebUI documents model access control as restricting models to specific users or groups.
• The workspace-model documentation treats "wrapper checked, restricted underlying model reached" as broken access control and recommends independent entries for curated deployments.
• The evaluation documentation describes arena mode as an evaluation/comparison feature that randomly selects models to compare, not as a feature that grants access to otherwise restricted models.