Vulnerability · Published Jul 14, 2026 · Assigned by GitHub_M
CVE-2026-45363`jwt` (Ruby gem) - empty-key HMAC bypass
Critical 9.1
In plain English
A critical-severity improper authentication in ruby-jwt from jwt. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | ruby-jwt | 2.5.0-1+deb12u1 | DEBIAN-CVE-2026-45363 |
| Debian:13 | ruby-jwt | 2.7.1-1+deb13u1 | DEBIAN-CVE-2026-45363 |
| Debian:14 | ruby-jwt | 3.2.0-1 | DEBIAN-CVE-2026-45363 |
| RubyGems | jwt | 3.2.0 | GHSA-c32j-vqhx-rx3x |
| RubyGems | jwt | 2.10.3 | GHSA-c32j-vqhx-rx3x |
| Ubuntu:22.04:LTS | ruby-jwt | no fix listed | UBUNTU-CVE-2026-45363 |
| Ubuntu:24.04:LTS | ruby-jwt | no fix listed | UBUNTU-CVE-2026-45363 |
| Ubuntu:26.04:LTS | ruby-jwt | no fix listed | UBUNTU-CVE-2026-45363 |
| Ubuntu:26.10 | ruby-jwt | no fix listed | UBUNTU-CVE-2026-45363 |
Affected products (as reported)
Weakness: CWE-287, CWE-326, CWE-1391 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
References
- https://github.com/jwt/ruby-jwt/security/advisories/GHSA-c32j-vqhx-rx3x x_refsource_CONFIRM
- https://github.com/jwt/ruby-jwt/commit/9820020869ad147b941e49d96ab8beba35532964 x_refsource_MISC
- https://github.com/jwt/ruby-jwt/commit/db560b769a07bd9724e77ff505011ac01872106f x_refsource_MISC
- https://github.com/jwt/ruby-jwt/releases/tag/v2.10.3 x_refsource_MISC
- https://github.com/jwt/ruby-jwt/releases/tag/v3.2.0 x_refsource_MISC
- https://lists.debian.org/debian-lts-announce/2026/09/msg00022.html