ADVISORIES
GEM
SEVERITY
CVSS v3.x: 9.1 (Critical)
PATCHED VERSIONS
- >= 1.1.1
DESCRIPTION
Overview
The authentication tag of encrypted JWEs can be brute forced, which may result in loss of confidentiality for those JWEs and provide ways to craft arbitrary JWEs.
Impact
- JWEs can be modified to decrypt to an arbitrary value
- JWEs can be decrypted by observing parsing differences
- The GCM internal GHASH key can be recovered
Am I Affected?
You are affected by this vulnerability even if you do not
use an AES-GCM encryption algorithm for your JWEs.
Patches
The version 1.1.1 fixes the issue by adding the tag length check for the AES-GCM algorithm.
Important: As the GHASH key could have leaked, you must rotate the encryption keys after upgrading to version 1.1.1.
References
Félix Charette talk at NorthSec 2025 about the issue