The flaw resides in Open WebUI’s knowledge search path, permitting any logged‑in user to submit arbitrary regex patterns. If a pattern contains backtracking constructs, it is run against every line of every reachable knowledge file with no execution limit. A crafted expression can monopolise a worker’s CPU, stall the event loop, and force the entire worker to become unavailable for all other users, resulting in a service outage.

Open WebUI products from version 0.9.6 up to 0.10.x are vulnerable. The affected component is identified as open-webui:open-webui. Any instance deployed with these releases is at risk until the software is updated beyond 0.10.x.

The CVSS score of 6.5 indicates a moderate severity. No EPSS score is currently available, and the vulnerability is not listed in CISA’s KEV catalog. The attack requires authentication and relies on the user ability to supply a regex pattern. While no public exploits have been reported, an attacker with a valid user account could easily trigger the backtracking, causing a denial of service to all users sharing the same worker.