This flaw is an authentication bypass (CWE-287) that allows an attacker holding any OAuth access token issued to any client registered with the same provider to exchange that token for an Open WebUI session. The /oauth/{provider}/token/exchange endpoint validates the provider’s userinfo endpoint without confirming which OAuth client the token was issued to, enabling an account takeover that grants full control of the victim’s account and access to all associated data.

The vulnerability impacts installations of open-webui:open-webui from version 0.8.0 up to and including 0.11.0 when ENABLE_OAUTH_TOKEN_EXCHANGE is enabled. The issue is fixed in release 0.11.0; upgrading to that or newer resolves the flaw.

With a CVSS score of 8.1 the flaw is classified as high severity. The EPSS score is not available, and it is not listed in the CISA KEV catalog, yet the attack vector is straightforward: any party capable of obtaining an OAuth access token for any client of the identity provider can exploit this flaw. The attacker can gain full user-level access without needing credentials for the Open WebUI system itself, potentially compromising user data and system integrity. Because the flaw can be exercised remotely by merely possessing a token, the likelihood of exploitation remains significant for public or partially exposed deployments.