Authenticated instance stall via skill-mention regex backtracking
Published Jul 9, 2026 · Updated Jul 9, 2026
Regular expression denial of service in Open WebUI 0.9.2 through 0.9.6 allows remote authenticated users to stall the instance. SKILL_MENTION_RE and strip_re apply overlapping quantified character classes to an unterminated <$ skill mention, causing quadratic backtracking on the asyncio event loop. Any authenticated account can submit one chat message; the default single-worker deployment then stops serving all users until the worker is killed.
Summary
What happened
Regular expression denial of service in Open WebUI 0.9.2 through 0.9.6 allows remote authenticated users to stall the instance. SKILL_MENTION_RE and strip_re apply overlapping quantified character classes to an unterminated <$ skill mention, causing quadratic backtracking on the asyncio event loop. Any authenticated account can submit one chat message; the default single-worker deployment then stops serving all users until the worker is killed.
The record
- CVE
- CVE-2026-59220
- Published
- Jul 9, 2026
- Updated
- Jul 9, 2026
- Vendor
- Open WebUI
- Product
- Open WebUI
- Classifications
- CWE-1333, CAPEC-492, T1499.004
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 9, 2026CVE publishedPublication date reported by the CVE source.
- Jul 9, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 0.9.2, < 0.10.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Open WebUI skill-mention ReDoS proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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