Vulnerability Description
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.
CVSS Score
CRITICAL
Related Weaknesses (CWE)
References
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc
FAQ
What is CVE-2026-44351?
CVE-2026-44351 is a vulnerability with a CVSS score of 9.1 (CRITICAL). 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 ...
How severe is CVE-2026-44351?
CVE-2026-44351 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-44351?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.