ZITADEL is an open source identity management platform. Prior to 3.4.12 and 4.15.2, ZITADEL's external JWT Identity Provider validates a token's signature and issuer (iss) but not the audience (aud) claim, allowing a validly signed token from a trusted issuer for another relying party to be accepted by ZITADEL. This issue is fixed in versions 3.4.12 and 4.15.2.

Affected: Go: github.com/zitadel/zitadel

### Summary

An authentication bypass vulnerability was discovered in ZITADEL's external JWT Identity Provider (IdP) implementation.

When validating JSON Web Tokens (JWTs) from an external provider, ZITADEL properly checks the token's cryptographic signature and issuer (`iss`), but it fails to validate the audience (`aud`) claim.

As a result, any validly signed token from the trusted issuer will be accepted. An attacker who is a legitimate user of a completely separate service sharing the same enterprise Identity Provider can intercept or present their token for that service to ZITADEL, successfully authenticating as that user without authorization.

### Impact

In a controlled enterprise environment where Identity Providers are explicitly managed, the operational risk is localized. Exploitation requires that an attacker already possesses a valid standard user session token from a shared, trusted issuer intended for an entirely different relying party, limiting the vector to specific, rare cross-service setups where trust boundaries overlap.

### Affected Versions

Systems running one of the following versions are affected:

* **4.x**: `4.0.0` through `4.11.0` (including RC versions) * **3.x**: `3.0.0` through `3.4.11` (including RC versions)

### Patches

The vulnerability has been addressed in the latest releases, where a required audience can be set in the IdP configuration. Once provided, audience validation will be enforced.

* **4.x**: Upgrade to $\ge$ [4.15.2](https…