Apache Airflow FAB provider fails to validate the issuer and audience claims of the id_token it receives from the Authentik OAuth path. Because the audience claim is never checked, a token that an Authentik identity provider minted for another client application can be used against Airflow, allowing the attacker to authenticate as the user named in the token. This flaw permits an attacker who can acquire a valid token for any application served by the same Authentik instance to gain unauthorized access to Airflow, resulting in potential compromise of the Airflow deployment and the data or workflows it manages.

Deployments that use the FAB auth manager with Authentik OAuth are affected. The issue is present on systems where the same Authentik identity provider serves multiple applications, and an attacker possesses a token for one of those other applications. The vulnerability does not affect installations that have already applied the CVE-2026-75156 fix and use Authentik, provided they also upgrade to this version.

The vulnerability is exploitable through the standard OAuth flow; an attacker can submit a counterfeit id_token to the Airflow authentication endpoint. The EPSS score of < 1% and the fact that the vulnerability is not listed in CISA KEV indicate a low probability of exploitation, but the potential impact is significant because it allows arbitrary authentication. The flaw exists because the code path never checks the audience claim, meaning that clients can be impersonated across applications served by the same Authentik provider.