The Apache Airflow FAB provider failed to verify the issuer and audience claims of Azure AD id_tokens during OAuth authentication. Because the provider trusts Microsoft’s multi‑tenant JWKS endpoint, any token minted in an attacker‑controlled Azure tenant passes signature validation, then carries the attacker’s username and role assignments into Airflow. This flaw allows an attacker who can register an Azure tenant to authenticate to the Airflow UI with full privileges, raising the risk of unauthorized data access, configuration changes, and potential data exfiltration.

Apache Software Foundation’s Apache Airflow FAB provider is impacted for all releases from 3.7.3 through 3.8.0 inclusive. Operators who applied the CVE‑2026‑59243 fix, which only added signature verification, remain vulnerable because issuer/audience checks were not added; therefore any version containing that fix within the range must be upgraded to 3.8.1 or later to remediate the issue.

The vulnerability carries a CVSS score of 9.1, indicating critical severity, and is not listed in CISA’s KEV catalog. Exploitation requires only the ability to create an Azure tenant and issue a signed id_token, with no need for internal network access to Airflow. The attack vector is straightforward: an attacker registers a tenant, generates an id_token, and authenticates to Airflow, bypassing tenant restrictions and gaining legitimate access to the system.