CVE-2026-59220 Open WebUI vulnerability
Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.9.2 before 0.10.0, the SKILL_MENTION_RE and strip_re regular expressions in backend/open_webui/utils/middleware.py parsed <$skillId|label> skill mentions with overlapping quantifiers, allowing an authenticated chat message containing <$ without a closing > to trigger quadratic backtracking and block the asyncio event loop. This issue is fixed in version 0.10.0.
Quick answer
Open WebUI should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- Open WebUI >=0.9.2 <0.10.0
Fixed versions
- 0.10.0
How to fix it
CVE-2026-59220 affects Open WebUI 0.9.2 before 0.10.0, where skill mention regular expressions could trigger quadratic backtracking and block the asyncio event loop with crafted chat messages. Prioritize shared or internet-facing Open WebUI deployments because the issue can affect realtime sessions, model access, knowledge files, terminal proxy access, or sensitive settings depending on the endpoint. Upgrade Open WebUI to 0.10.0 or a later supported release. Limit untrusted chat message size and rate until patched.
- Inventory all Open WebUI deployments, containers, workers, reverse proxies, realtime Socket.IO endpoints, terminal integrations, and configured model providers.
- Identify Open WebUI 0.9.2 before 0.10.0 and schedule an upgrade to Open WebUI 0.10.0 or later for CVE-2026-59220.
- Upgrade Open WebUI to 0.10.0 or a later supported release, rebuild images, restart services, and clear stale application caches where applicable.
- Limit untrusted chat message size and rate until patched.
- Review Open WebUI roles, verified-user status, model permissions, knowledge base permissions, terminal connections, Redis token revocation, and provider credentials for unnecessary exposure.
- Review application, reverse proxy, Socket.IO, terminal backend, and audit logs for suspicious endpoint use matching the affected workflow.
- If credential or data exposure is suspected, revoke sessions and API keys, rotate provider credentials and webhooks, remove malicious content, and preserve request logs before cleanup.
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Verify the fix
- Confirm every Open WebUI deployment reports version 0.10.0 or later and that old images or services are no longer running.
- Confirm malformed <$ skill mention messages are processed in bounded time.
- Confirm authorization checks, token revocation, role checks, and response filtering match the intended policy for affected users and endpoints.
- Run focused regression checks against the affected endpoint and confirm unauthorized or malformed requests fail safely.
- Document patched image digests, configuration changes, credential rotation, log review, and test evidence.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-59220?
Open WebUI versions listed as affected should be reviewed: Open WebUI >=0.9.2 <0.10.0.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.