Inefficient regular expression complexity in Open WebUI - #VU135957
Published: June 30, 2026
Vulnerability identifier: #VU135957
CSH Severity: Low
CVSS v4.0: 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/E:U/U:Clear
CVE-ID: N/A
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Open WebUI
Affected software:
Open WebUI
Open WebUI
Detailed vulnerability description
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.
Remediation
Install security update from vendor's website.