Description
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.
References6
- github.com/jwt/ruby-jwt/commit/9820020869ad147b941e49d96ab8beba…
- github.com/jwt/ruby-jwt/commit/db560b769a07bd9724e77ff505011ac0…
- github.com/jwt/ruby-jwt/releases/tag/v2.10.3
- github.com/jwt/ruby-jwt/releases/tag/v3.2.0
- github.com/jwt/ruby-jwt/security/advisories/GHSA-c32j-vqhx-rx3x
- lists.debian.org/debian-lts-announce/2026/09/msg00022.html
Metrics
- CVSS 3.1
-
9.1
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 0% percentile: 31 · as of 15 November 2026
- CWE
- CWE-287CWE-326CWE-1391
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