Open WebUI contains an IDOR in the channels message update and delete endpoints. The backend performs only channel‑level authorization, missing message‑owner validation. As a result, an authenticated user who can read a channel can modify or delete any message in that channel, regardless of who sent it. This breaks integrity and potentially confidentiality of user content.

Any installation of open-webui:open-webui before release 0.6.19 is affected. The fix was applied in 0.6.19 and later versions.

The CVSS score of 7.1 indicates moderate to high severity. EPSS is not available and the vulnerability is not listed in the CISA KEV catalog, suggesting it has not yet been widely exploited in the wild. An attacker must first authenticate to the system and obtain read access to a channel; thereafter the exploit can be performed via direct API calls. The impact is limited to unauthorized modification or deletion of messages, but the consistency and trustworthiness of logged content could be undermined in multi‑user environments.