CVE-2026-75156: Apache Airflow FAB provider: FAB Azure AD OAuth: id_token issuer/audience not validated — cross-tenant authentication bypass

Apache Airflow FAB provider versions 3.7.3 through 3.8.0 do not validate the issuer or audience of Azure AD idtokens during OAuth login. Deployments are affected only when the FAB auth manager is configured with Azure AD as an OAuth provider. Because the signing keys are fetched from Microsoft's multi-tenant JWKS endpoint, an idtoken minted in any Azure tenant — including one the attacker creates — passes signature verification, and the username and role assignments are then read from that attacker-controlled token. Anyone able to register an Azure tenant can therefore authenticate to the Airflow UI with no prior access to the deployment.

The fix for CVE-2026-59243 was incomplete, and this advisory closes the remaining gap: that fix made the provider verify the idtoken signature, but did not add issuer or audience checks. Operators who already applied the CVE-2026-59243 fix are still affected and must upgrade again — 3.7.3 is the release that shipped that fix, so every version containing it falls inside this affected range. Upgrade to apache-airflow-providers-fab 3.8.1 or later.