rules:
  - id: auth.java.jwt.untrusted-verify-key
    languages:
      - java
    severity: ERROR
    message: |
      Untrusted request input flows into the JWT verification key. When the
      attacker controls the key, they sign their own forged token and supply the
      matching key, so every token "verifies", a complete authentication bypass
      (CWE-347, Improper Verification of Cryptographic Signature).

      The verification key must be fixed server-side. Resolve it from trusted
      configuration, a keystore, or a vetted key set keyed by a validated `kid`,
      never from `request.getParameter(...)` / `request.getHeader(...)` or a
      `@RequestParam` / `@RequestHeader` value.
    # Taint mode with the sink FOCUSED on the key argument, never the token. The
    # token is supposed to come from the request, so focusing on it would
    # false-positive on every correct call; focusing on the key fires only when
    # the attacker controls verification itself. Sources are the servlet request
    # accessors that return raw client input. A key fetched from a keystore
    # (`KeyStore.getKey(...)`) clears the taint.
    mode: taint
    pattern-sources:
      - pattern: $REQ.getParameter(...)
      - pattern: $REQ.getParameterValues(...)
      - pattern: $REQ.getHeader(...)
      - pattern: $REQ.getHeaders(...)
    pattern-sanitizers:
      - pattern: $KS.getKey(...)
    pattern-sinks:
      # jjwt: the signing/verification key passed to the parser.
      - patterns:
          - pattern-either:
              - pattern: $P.setSigningKey($SINK)
              - pattern: $P.verifyWith($SINK)
          - focus-metavariable: $SINK
      # nimbus-jose-jwt: the HMAC secret handed to the verifier.
      - patterns:
          - pattern: new MACVerifier($SINK)
          - focus-metavariable: $SINK
    metadata:
      oauthlint-rule-id: AUTH-JAVA-JWT-003
      oauthlint-doc-url: https://oauthlint.dev/rules/java-jwt-untrusted-verify-key
      category: security
      cwe: CWE-347
      owasp: API2:2023
      llm-prevalence: LOW
      technology:
        - jjwt
        - nimbus-jose-jwt
      references:
        - https://cwe.mitre.org/data/definitions/347.html
        - https://datatracker.ietf.org/doc/html/rfc7518#section-3.1
        - https://owasp.org/www-project-api-security/