Inefficient regular expression complexity in Open WebUI - CVE-2026-59220
Published: June 30, 2026
Vulnerability identifier: #VU135957
CSH Severity: Low
CVSS v4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-59220
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in skill-mention regexes in backend/open_webui/utils/middleware.py when processing chat messages or retrieved content containing a skill-mention pattern without a closing >. A remote user can send a specially crafted chat message to cause a denial of service.
The affected regex processing runs synchronously on the asyncio event loop on every chat completion with no feature gate, and benign retrieved content such as a RAG chunk or tool output can also trigger the issue.
Affected software
Open WebUI
How to mitigate CVE-2026-59220
Install security update from vendor's website.
Open WebUI - update to 0.10.0