jose vulnerable to untrusted JWK header key acceptance during signature verification
Date: 2026-03
Affected: pub/jose
Attack vector: other
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-34240
CWE: CWE-347
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)

### Impact A vulnerability in `jose` versions up to and including `0.3.5` could allow an unauthenticated, remote attacker to forge valid JWS/JWT tokens by using a key embedded in the JOSE header (`jwk`). The vulnerability exists because key selection could treat header-provided `jwk` as a verification candidate even when that key was not present in the trusted key store. Since JOSE headers are untrusted input, an attacker could exploit this by creating a token payload, embedding an attacker-controlled public key in the header, and signing with the matching private key. Applications using affected versions for token verification are impacted. ### Patches Upgrade to `0.3.5+1` or later. ### Workarounds Reject tokens where header `jwk` is present unless that `jwk` matches a key already present in the application's trusted key store. ### Resources Fix commit: [fix: improved key resolution in JsonWebKeyStore](https://github.com/appsup-dart/jose/commit/b07799aac1f56a9a21483feac026272aab30cc5d)


Mitigations:

Architectural layers (MAESTRO):