GHSA-2f54-p244-32q6: Open WebUI: Any authenticated user can stall a worker via a knowledge-search pattern that backtracks catastrophically

Summary The built-in knowledge search tools let a chat participant choose the pattern used to grep knowledge files. Patterns containing regex metacharacters were compiled with Python's backtracking re engine and run against every line of every reachable file, with no time limit anywhere on that path. A single crafted pattern and a single short line of matching text pin one CPU core for as long as the attacker wants, and because the search runs synchronously inside the event loop, that worker serves nobody else while it spins. Preconditions - Default configuration. The knowledge builtin tool group is enabled by default, and with ENABLE_KB_EXEC at its default of False the model is handed grep_knowledge_files, which is the affected path. - Any authenticated user, no elevated role and no workspace permission. - One file the attacker can read. USER_PERMISSIONS_CHAT_FILE_UPLOAD defaults to true and a user always has read access to their own upload, so both halves of the input are attacker-supplied. - A model willing to call the tool with the attacker's literal pattern. This is the one non-deterministic step: it is reliable in practice by instructing the model in your own chat, but it is not guaranteed on a given turn. - Deployments running with UVICORN_WORKERS at its default of 1 lose the whole instance; multi-worker deployments lose one worker per request. Impact Availability, against every other user of the affected worker. Cost scales exponentially with the length of the matching text: measured on the vulnerable code, a 24 character subject takes 1.2s, 28 takes 19s and 30 takes 74s, and a 40 character subject extrapolates to roughly a day of CPU. The same subject against a literal pattern takes under a microsecond. There is no confidentiality or integrity effect, and no data is read or altered. Fix Fixed in 0.11.0 by https://github.com/open-webui/open-webui/pull/27471. Pattern matching moved from re to the regex engine, which supports a per-search timeout, and every