CVE-2026-44569: Open WebUI: Insecure Message Access Breaks Authorization

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.6.19, there's an IDOR in the channels message management system that allows authenticated users to modify or delete any message within channels they have read access to. The vulnerability exists in the message update and delete endpoints, which implement channel-level authorization but completely lack message ownership validation. While the frontend correctly implements ownership checks (showing edit/delete buttons only for message owners or admins), the backend APIs bypass these protections by only validating channel access permissions without verifying that the requesting user owns the target message. This creates a client-side security control bypass where attackers can directly call the APIs to modify other users' messages. This vulnerability is fixed in 0.6.19.