Executive brief
Open WebUI is a user interface for interacting with large language models. A vulnerability in its channel messaging system allows any authenticated user to modify messages sent by other users in standard channels. This could lead to the unauthorized alteration of chat history or shared information, potentially impacting the integrity of communications within the platform.
Technical details
An improper authorization vulnerability exists in Open WebUI's channel message update endpoint. In standard channels (non-group/DM), the `POST /api/v1/channels/{channel_id}/messages/{message_id}/update` endpoint incorrectly validates permissions using a 'read' check instead of a 'write' or ownership check. When `access_control` is set to None, the `has_access` function evaluates to True for any user with read access, allowing them to modify messages they do not own. An attacker requires an authenticated account and the target `message_id` to exploit this flaw. The issue is addressed in version 0.8.6 by enforcing stricter write permission requirements.
Affected products
- Open WebUI open-webui <= 0.8.5
Timeline
- 2026-05-11: advisory: GitHub Advisory published
- 2026-05-11: patched: First patched version 0.8.6 released