CVE-2026-107724: Nearform Fast-Jwt

High severity, CVSS 7.4. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• Nearform Fast-Jwt: from 6.2.4, before 6.3.0 (fixed in 6.3.0)

Published 2026-10-08. Last modified 2026-10-09.