CVE-2026-45363

CVE-2026-45363 is a high-severity improper authentication vulnerability in jwt (rubygems), affecting versions >= 3.0.0, < 3.2.0. It is fixed in 3.2.0, 2.10.3.

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Summary

ruby-jwt: Empty-key HMAC bypass; cross-language sibling of CVE-2026-44351

JWT.decode(token, '', true, algorithm: 'HS256') accepts an attacker-forged token.
OpenSSL::HMAC.digest('SHA256', '', payload) returns a valid digest under an empty key, and no raise InvalidKeyError if key.empty? precondition exists in the HMAC algorithm.

JWT.decode(token, "", true, algorithm: 'HS256')
  -> JWA::Hmac.verify(verification_key: "", ...)
  -> OpenSSL::HMAC.digest('SHA256', "", signing_input) == signature

The same path is reached when a keyfinder block or key_finder: argument returns "", nil, or an
array containing nil for an unknown key. JWT::Decode#find_key only rejects literal nil and empty
arrays, and JWT::JWA::Hmac silently coerces nil to "" (signing_key ||= '') before signing.

JWT.decode(token, nil, true, algorithms: ['HS256']) { |_h| "" }
  -> find_key returns ""               # "" && !Array("").empty? == true
  -> JWA::Hmac.verify(verification_key: "", ...)
  -> verifies

Common application patterns that produce the unsafe value: redis.get("kid:#{kid}").to_s, ORM string columns with default: '', ENV['SECRET'] || '', Hash.new('') lookups, [primary, fallback] where fallback may be nil. Applications passing a non-empty static key:, or whose keyfinder returns nil / raises on miss, are not affected.

The existing enforce_hmac_key_length option would block this but defaults to false. On OpenSSL ≥ 3.5 the empty-key HMAC.digest call no longer raises, so the OpenSSL-3.0 rescue in JWA::Hmac#sign does not fire.

Affects HS256/HS384/HS512 via both JWT.decode (positional key and block keyfinder) and
JWT::EncodedToken#verify_signature!(key_finder:)

Impact

The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.

CVE-2026-45363 has a CVSS score of 7.4 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.2.0, 2.10.3); upgrading removes the vulnerable code path.

Affected versions

jwt (>= 3.0.0, < 3.2.0) jwt (< 2.10.3)

Security releases

jwt → 3.2.0 (rubygems) jwt → 2.10.3 (rubygems)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Upgrade the following packages to resolve this vulnerability:

jwt to 3.2.0 or later; jwt to 2.10.3 or later

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

  1. What is CVE-2026-45363? CVE-2026-45363 is a high-severity improper authentication vulnerability in jwt (rubygems), affecting versions >= 3.0.0, < 3.2.0. It is fixed in 3.2.0, 2.10.3. The application does not adequately verify the identity of a user, device, or process before granting access.
  2. How severe is CVE-2026-45363? CVE-2026-45363 has a CVSS score of 7.4 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which versions of jwt are affected by CVE-2026-45363? jwt (rubygems) versions >= 3.0.0, < 3.2.0 is affected.
  4. Is there a fix for CVE-2026-45363? Yes. CVE-2026-45363 is fixed in 3.2.0, 2.10.3. Upgrade to this version or later.
  5. Is CVE-2026-45363 exploitable, and should I be worried? Whether CVE-2026-45363 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2026-45363 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2026-45363?
    • Upgrade jwt to 3.2.0 or later
    • Upgrade jwt to 2.10.3 or later

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