CVE-2026-107720: Nearform Fast-Jwt

High severity, CVSS 7.4. EPSS: 0.3% chance of exploitation in the next 30 days.

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1.

Affected products

• Nearform Fast-Jwt: before 6.3.1 (fixed in 6.3.1)

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