Description


fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.2.4, fast-jwt can classify raw serialized public JWK or JWKS JSON as an HMAC secret because src/crypto.js performDetectPublicKeyAlgorithms treats non-PEM strings as symmetric key material. If HS256 is explicitly allowed or inferred, an attacker who knows the exact serialized public-key bytes can use those bytes as an HMAC key and create a token containing arbitrary claims that createVerifier accepts. Serialization ordering or whitespace differences can prevent exploitation, and applications using supported PEM keys with an asymmetric-only algorithm allowlist are not affected. This issue is fixed in version 6.3.0.

Related CPE's


Could not find any relations

Weaknesses



CWE-347

CVSS impact metrics


CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

7.4 · High

Information


Source identifier

[email protected]

Vulnerability status

Deferred

Published

2026-10-08T22:17:28.800Z

10 hours ago

Last modified

2026-10-08T22:17:28.930Z

10 hours ago