CVE-2026-107724 — fast-jwt provides fast JSON Web Token (JWT) implementation.
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.
CVSS v3.1 base metrics
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:NHigh severity
Band computed from the CVSS base score, not the source's own label — so it means the same thing across every feed.
AV
Network
Attack Vector
AC
High
Attack Complexity
PR
None
Privileges Required
UI
None
User Interaction
S
Unchanged
Scope
C
High
Confidentiality
I
High
Integrity
A
None
Availability
References
- advisory[email protected]https://github.com/nearform/fast-jwt/commit/10f9591349199ed2ab9fa1748ce92cdca697f6cf
- advisory[email protected]https://github.com/nearform/fast-jwt/pull/636
- advisory[email protected]https://github.com/nearform/fast-jwt/releases/tag/v6.3.0
- advisory[email protected]https://github.com/nearform/fast-jwt/security/advisories/GHSA-g3jj-5cmm-3hxx
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