The flaw occurs in the OAuth token exchange path of Open WebUI. When a provider access token is exchanged, the service creates a session even when the user’s email domain is on the deny list or the role policy excludes them. This bypasses the domain allowlist that normally protects users. As a result, an attacker who can obtain a valid provider token can gain access to an account that would otherwise be denied, exposing sensitive content and configuration within the platform.

Open WebUI versions 0.8.0 through 0.9.0 are affected. Any deployment using these versions and relying on the OAuth token exchange endpoint is at risk until the fix in 0.9.0 is applied.

The CVSS score of 6.5 indicates a moderate severity. The EPSS score is not available and the issue is not listed in KEV, suggesting limited current exploitation. Exploitation requires a provider access token, which can be generated by the attacker or stolen from a legitimate user. The attack vector is remote, using the public token exchange endpoint. Due to the lack of server-side enforcement of the allowlist, the flaw provides unauthorized authentication. Organizations should promptly apply the 0.9.0 update to mitigate.