PYSEC-2026-2726 Open WebUI has Broken Access Control for Completions API

Summary Any user X can continue the conversation of any other user Y, as long as the Chat ID of Y is known. User X does not even need to be an admin to do so. Details A user just needs to use the API endpoint: /api/chat/completions with their own API key generated in OWUI and the Chat ID of anoth...