PYSEC-2026-3596 Open WebUI: ReDoS in skill-mention regexes causes whole-instance DoS on default config

Summary Two regexes in backend/openwebui/utils/middleware.py that parse skill-mention tags backtrack in On² on input that contains . Both run synchronously, on the asyncio event loop, on every chat completion with no feature gate. Because the default deployment is a single uvicorn worker, one suc...