Executive brief
Open WebUI, a user interface for AI models, is vulnerable to a denial-of-service attack. An authenticated user can provide a specially crafted search pattern that causes the system's processor to become stuck in an infinite loop. This can result in the entire application becoming unresponsive for all users, effectively shutting down the service.
Technical details
A Regular Expression Denial of Service (ReDoS) vulnerability exists in Open WebUI's knowledge search functionality. The `grep_knowledge_files` tool in `backend/open_webui/tools/builtin.py` uses Python's `re` engine to compile and execute user-provided patterns against files without a timeout. Because the search runs synchronously within the event loop, a pattern designed to trigger catastrophic backtracking (e.g., `(x|x)*y`) can exhaust CPU resources and block the worker process from handling other requests. The vulnerability is present in the default configuration where knowledge tools are enabled. It was fixed in version 0.11.0 by migrating to the `regex` engine and implementing a global 2-second matching budget per tool call.
Affected products
- Open WebUI open-webui >= 0.9.6, < 0.11.0
Timeline
- 2026-08-02: patched: Fix merged in PR 27471
- 2026-08-04: advisory: GitHub Advisory GHSA-2f54-p244-32q6 published