rules:
  - id: auth.ruby.jwt.missing-algorithm-allowlist
    languages:
      - ruby
    severity: WARNING
    message: |
      `JWT.decode` is called with verification enabled (`true`) but no
      `algorithm:` / `algorithms:` option, so the library trusts whatever `alg`
      the token header names. An attacker can switch the algorithm, e.g. present
      an `HS256` token signed with your RSA *public* key as if it were the HMAC
      secret, and the signature check passes (algorithm-confusion, CWE-347).

      Always pin the accepted algorithm(s):
        JWT.decode(token, key, true, { algorithm: 'HS256' })
        JWT.decode(token, public_key, true, { algorithms: ['RS256'] })
      ruby-jwt's own docs mark this allow-list as mandatory for safe decoding.
    # Strict arity: match the exact 3-argument form `JWT.decode(t, k, true)`.
    # A 4th options argument (where the algorithm allow-list would live) makes
    # this pattern not apply, so a correctly-pinned call never fires. The
    # `true` literal in the verify slot is required, which also excludes the
    # `false` (verification off) and `nil` (no-key) forms handled elsewhere.
    patterns:
      - pattern: JWT.decode($T, $K, true)
    paths:
      exclude:
        - "**/spec/**"
        - "**/test/**"
        - "**/*_spec.rb"
        - "**/*_test.rb"
        - "**/features/**"
    metadata:
      oauthlint-rule-id: AUTH-RUBY-JWT-002
      oauthlint-doc-url: https://oauthlint.dev/rules/ruby-jwt-missing-algorithm-allowlist
      category: security
      cwe: CWE-347
      owasp: API2:2023
      llm-prevalence: HIGH
      technology:
        - ruby-jwt
      references:
        - https://github.com/jwt/ruby-jwt
        - https://auth0.com/blog/critical-vulnerabilities-in-json-web-token-libraries/