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.
History

Thu, 14 May 2026 19:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 13 May 2026 22:00:00 +0000

Type Values Removed Values Added
First Time appeared Nearform
Nearform fast-jwt
Vendors & Products Nearform
Nearform fast-jwt

Wed, 13 May 2026 20:00:00 +0000

Type Values Removed Values Added
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.
Title fast-jwt: Empty HMAC secret accepted via async key resolver - JWT auth bypass
Weaknesses CWE-1391
CWE-287
CWE-326
References
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-05-14T18:13:32.626Z

Reserved: 2026-05-05T19:52:59.148Z

Link: CVE-2026-44351

cve-icon Vulnrichment

Updated: 2026-05-14T18:13:23.007Z

cve-icon NVD

Status : Deferred

Published: 2026-05-13T20:16:22.860

Modified: 2026-05-14T19:16:37.050

Link: CVE-2026-44351

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-13T22:15:09Z