rules:
  - id: auth.csharp.crypto.insecure-random
    languages:
      - csharp
    severity: ERROR
    message: |
      A security-sensitive value is generated with `System.Random` or
      `Guid.NewGuid()` inside a token/secret/OTP generator. `System.Random` is a
      non-cryptographic PRNG seeded from the clock: its output is predictable and
      its state is recoverable from a few samples, so an attacker can reconstruct
      the "random" secret (CWE-338). `Guid.NewGuid()` is not guaranteed to be
      cryptographically random either. AI tools paste these in because they look
      random enough.

      Use `System.Security.Cryptography.RandomNumberGenerator` instead, e.g.
      `RandomNumberGenerator.GetBytes(32)` (then Base64/hex encode) or
      `RandomNumberGenerator.GetInt32(...)`.
    patterns:
      - pattern-either:
          - pattern: new System.Random(...)
          - pattern: new Random(...)
          - pattern: Guid.NewGuid()
          - pattern: System.Guid.NewGuid()
      - pattern-inside: |
          $RET $METHOD(...) { ... }
      - metavariable-regex:
          metavariable: $METHOD
          regex: (?i).*(token|secret|otp|apikey|api_?key|reset|nonce|passcode|verificationcode|salt).*
    paths:
      exclude:
        - "**/test/**"
        - "**/*Test.cs"
        - "**/*Tests.cs"
    metadata:
      oauthlint-rule-id: AUTH-CSHARP-CRYPTO-001
      oauthlint-doc-url: https://oauthlint.dev/rules/csharp-crypto-insecure-random
      category: security
      cwe: CWE-338
      owasp: A02:2021
      llm-prevalence: HIGH
      technology:
        - dotnet
      references:
        - https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator
        - https://cwe.mitre.org/data/definitions/338.html