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PYSEC-2026-4119
open-webuiSummary
Open WebUI's OAuth token exchange endpoint issues a session for a provider access token without applying the email domain allowlist that the normal OAuth login callback enforces. An account whose email domain the login callback would refuse could still obtain a working session through this endpoint.
Preconditions
ENABLE_OAUTH_TOKEN_EXCHANGE=True. It is disabled by default, so a default deployment is not affected.OAUTH_ALLOWED_DOMAINSset to something other than*. Deployments without a domain allowlist are not affected.- A valid, unexpired access token on the configured provider.
- An Open WebUI account already linked to that provider subject, or an account with a matching email when
OAUTH_MERGE_ACCOUNTS_BY_EMAILis enabled. This endpoint never creates accounts, so a token for a subject with no existing account is rejected.
Impact
An admin who narrows the domain allowlist expects users outside it to lose access at their next sign-in. The login callback does deny them. Token exchange kept issuing sessions, so a user whose domain was removed retained working access as their existing account at its existing role. The endpoint cannot create an account and cannot raise anyone's role, so this grants continued access rather than new or elevated access.
Fix
fb5ef978b, released in 0.9.0, adds the same domain allowlist check to the token exchange endpoint that the login callback runs, and denies the exchange with 403 when the email domain is not allowed. Upgrading restores the check with no further action.
Root cause
The affected component is the OAuth token exchange endpoint in backend/open_webui/routers/auths.py, present in builds from 0.8.0 onward.
The endpoint was added as a second entry point into the same session-issuing path the OAuth login callback uses, but it re-implemented only the identity lookup and not the policy checks surrounding it. The domain allowlist check lived inside the callback's own body rather than in shared code, so the second caller inherited none of it.
Credits
@Classic298
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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