Open WebUI: Unauthenticated requests can stall the server via uncached OIDC fetches in back-channel logout
Open WebUI
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- Severity
- High, CVSS 7.5
- CVSS vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Record
- CVE-2026-87011
- Affects
- Open WebUI
- Known exploited
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Published
- Record first published by the source
- September 9, 2026
- Source last modified
- September 15, 2026
Description
Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.9.0 until 0.11.1, the unauthenticated POST /oauth/backchannel-logout handler in backend/open_webui/utils/oauth.py fetched the OIDC discovery document and signing keys before validating a submitted logout token. Each request repeated uncached network fetches, and the signing-key lookup blocked the async event loop, so requests carrying invalid tokens could stall the single-worker instance and amplify traffic to the identity provider when ENABLE_OAUTH_BACKCHANNEL_LOGOUT was enabled. This issue is fixed in version 0.11.1.
Description quoted from the NVD record.
Who is affected
Open WebUI is a chat program for AI tools that organizations run on their own servers. This flaw affects versions 0.9.0 to before 0.11.1, and only when the option that lets your outside sign-in service log people out of Open WebUI automatically is turned on. In that setup, anyone who can reach the server, without logging in, can send invalid logout requests that freeze an installation running as a single process and send repeated extra traffic to your sign-in service. This flaw is rated High.
What to do
- Find out who installed or runs Open WebUI for your organization: a staff member, a volunteer, or an IT provider or vendor.
- If someone in your organization runs it, ask them to update Open WebUI to version
0.11.1, which fixes this flaw. - If an IT provider or vendor runs it for you, send them this advisory and ask when the update will be done.
- Ask whoever runs it whether the automatic logout option linked to your sign-in service is turned on. If it is, treat the update as urgent, because that is the setup this flaw affects.
Analysis written from the source record as of September 15, 2026 and reviewed before publishing.