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CVE-2026-45363

`jwt` (Ruby gem) - empty-key HMAC bypass

CVSS 3.1 9.1 CRITICALCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-45363

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-45363

Published

ruby-jwt

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "jwt",
                    "product": "ruby-jwt",
                    "versions": [
                        {
                            "version": "< 2.10.3",
                            "status": "affected"
                        },
                        {
                            "version": ">= 3.0.0, < 3.2.0",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON