mcp-server-semgrep/semgrep-rules/csharp/dotnet/security/use_weak_rng_for_keygeneration.yaml

MCP Server for Semgrep Integration - static code analysis with AI

rules:
- id: use_weak_rng_for_keygeneration
  message: You are using an insecure random number generator (RNG) to create a cryptographic key. System.Random
    must never be used for cryptographic purposes. Use System.Security.Cryptography.RandomNumberGenerator
    instead.
  severity: ERROR
  metadata:
    likelihood: HIGH
    impact: MEDIUM
    confidence: HIGH
    category: security
    cwe:
    - 'CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)'
    owasp:
    - A02:2021 - Cryptographic Failures
    references:
    - https://learn.microsoft.com/en-us/dotnet/api/system.random?view=net-6.0#remarks
    - https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.randomnumbergenerator?view=net-6.0
    - https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.aesgcm?view=net-6.0#constructors
    - https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.symmetricalgorithm.key?view=net-6.0#system-security-cryptography-symmetricalgorithm-key
    subcategory:
    - vuln
    technology:
    - .net
  languages:
  - csharp
  mode: taint
  pattern-sources:
  - patterns:
    - pattern-inside: (System.Random $RNG).NextBytes($KEY); ...
    - pattern: $KEY
  pattern-sinks:
  - pattern-either:
    - patterns:
      - pattern: ($KEYTYPE $CIPHER).Key = $SINK;
      - focus-metavariable: $SINK
      - metavariable-pattern:
          metavariable: $KEYTYPE
          pattern-either:
          - pattern: SymmetricAlgorithm
          - pattern: Aes
          - pattern: Rijndael
          - pattern: DES
          - pattern: TripleDES
          - pattern: RC2
    - pattern: new AesGcm(...)
    - pattern: new AesCcm(...)
    - pattern: new ChaCha20Poly1305(...)