rules:
  - id: auth.kotlin.jwt.decode-without-verify
    languages:
      - kotlin
    severity: WARNING
    message: |
      A JWT is decoded but its signature is never verified. Auth0 java-jwt's
      `JWT.decode(token)` only base64-decodes the token (it does NOT check the
      signature), so any claim it exposes (subject, roles, expiry) is fully
      attacker-controlled (CWE-345). This is a common AI-generated mistake:
      `JWT.decode(...)` is reached for to "read the claims" and its result is
      trusted as if it had been verified.

      Verify the signature before reading any claim. With Auth0 java-jwt build a
      verifier and call it:
        `JWT.require(Algorithm.HMAC256(secret)).withIssuer(iss).withAudience(aud).build().verify(token)`
      The `DecodedJWT` returned by `verify(...)` is the only trustworthy one.
    # Auth0 java-jwt (com.auth0.jwt): JWT.decode(token) returns an UNVERIFIED
    # DecodedJWT. The verified path is JWT.require(alg).build().verify(token),
    # which uses .verify(...), not .decode(...), so it is not matched.
    pattern-either:
      - pattern: com.auth0.jwt.JWT.decode($T)
      - pattern: JWT.decode($T)
    metadata:
      oauthlint-rule-id: AUTH-KOTLIN-JWT-002
      oauthlint-doc-url: https://oauthlint.dev/rules/kotlin-jwt-decode-without-verify
      category: security
      cwe: CWE-345
      owasp: API2:2023
      llm-prevalence: HIGH
      technology:
        - java-jwt
      references:
        - https://github.com/auth0/java-jwt#decode-a-token
        - https://datatracker.ietf.org/doc/html/rfc8725#section-3.1
        - https://cwe.mitre.org/data/definitions/345.html