rules:
  - id: auth.py.crypto.passlib-weak-scheme
    languages:
      - python
    severity: ERROR
    message: |
      passlib configured with a weak or plaintext password scheme.

      A `CryptContext` lists a password hashing scheme that is broken for
      storing credentials: unsalted or fast digests (`hex_md5`, `hex_sha1`,
      `hex_sha256`, `md5_crypt`, `ldap_md5`), legacy `des_crypt`, or outright
      `plaintext` / `ldap_plaintext`. These are trivially brute-forced or
      reversed, so any leaked hash exposes the underlying password (CWE-916).

      Use a slow, salted, memory-hard scheme as the default, e.g.
      `CryptContext(schemes=["argon2"])` or
      `CryptContext(schemes=["bcrypt"])`. Keep a weak scheme only as a
      `deprecated` verifier during migration, never as an active hashing scheme.
    # Match the passlib `CryptContext(schemes=[...])` config where any element of
    # the schemes list is in a CLOSED list of genuinely broken schemes. The
    # `"$SCHEME"` string-literal metavariable captures each list element's text,
    # and the anchored metavariable-regex matches ONLY the weak names, so modern
    # schemes (bcrypt, argon2, scrypt, pbkdf2_sha256, ...) never fire.
    patterns:
      - pattern: CryptContext(..., schemes=[..., "$SCHEME", ...], ...)
      - metavariable-regex:
          metavariable: $SCHEME
          regex: ^(md5_crypt|des_crypt|plaintext|hex_md5|hex_sha1|hex_sha256|ldap_md5|ldap_plaintext)$
    metadata:
      oauthlint-rule-id: AUTH-PY-CRYPTO-001
      oauthlint-doc-url: https://oauthlint.dev/rules/py-crypto-passlib-weak-scheme
      category: security
      cwe: CWE-916
      owasp: A02:2021
      llm-prevalence: MEDIUM
      technology:
        - passlib
      references:
        - https://passlib.readthedocs.io/en/stable/lib/passlib.context.html
        - https://cwe.mitre.org/data/definitions/916.html