CVE-2026-44351
CriticalSummary
In versions prior to 6.2.4, the fast-jwt library has a critical authentication-bypass vulnerability that allows unauthenticated attackers to forge arbitrary JWTs accepted as authentic.
Risk Assessment
Organizations may be exposed to unauthorized access and data manipulation, potentially leading to serious security breaches.
Recommendation
It is recommended to update the fast-jwt library to version 6.2.4 or later to mitigate this vulnerability.
Original NVD description (English source)
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows any unauthenticated attacker to forge arbitrary JWTs that are accepted as authentic. When the application's key resolver returns an empty string (''), for example via the common keys[decoded.header.kid] || '' JWKS-style fallback, fast-jwt converts it to a zero-length Buffer, hands it to crypto.createSecretKey, derives allowedAlgorithms = ['HS256','HS384','HS512'] from it, and then verifies the token's signature against an empty-key HMAC. The attacker simply computes HMAC-SHA256(key='', input='${header}.${payload}'), which Node accepts without complaint — and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4.