CVE-2026-45363: Jwt Ruby-Jwt

Critical severity, CVSS 9.1. EPSS: 0.4% chance of exploitation in the next 30 days.

ruby-jwt is a Ruby implementation of the RFC 7519 OAuth JSON Web Token standard. Prior to 2.10.3 and 3.2.0, JWT.decode(token, '', true, algorithm: 'HS256') accepts an attacker-forged token because OpenSSL::HMAC.digest('SHA256', '', payload) returns a valid digest under an empty key and no empty-key precondition exists in the HMAC algorithm. The same path is reached when a keyfinder block or key_finder: argument returns an empty string, nil, or an array containing nil for an unknown key, affecting HS256, HS384, and HS512 verification through JWT.decode and JWT::EncodedToken#verify_signature!. This issue is fixed in versions 2.10.3 and 3.2.0.

Affected products

• Jwt Ruby-Jwt: before 2.10.3 (fixed in 2.10.3); from 3.0.0, before 3.2.0 (fixed in 3.2.0)

Published 2026-07-14. Last modified 2026-09-19.