mcp-server-semgrep/semgrep-rules/javascript/express/security/express-expat-xxe.yaml

MCP Server for Semgrep Integration - static code analysis with AI

rules:
- id: express-expat-xxe
  message: >-
    Make sure that unverified user data can not reach the XML Parser, as it
    can result in XML External or Internal Entity (XXE) Processing
    vulnerabilities.
  options:
    interfile: true
  metadata:
    interfile: true
    owasp:
    - A04:2017 - XML External Entities (XXE)
    - A05:2021 - Security Misconfiguration
    cwe:
    - 'CWE-611: Improper Restriction of XML External Entity Reference'
    asvs:
      section: V5 Validation, Sanitization and Encoding
      control_id: 5.5.2 Insecue XML Deserialization
      control_url: https://github.com/OWASP/ASVS/blob/master/4.0/en/0x13-V5-Validation-Sanitization-Encoding.md#v55-deserialization-prevention
      version: '4'
    references:
    - https://github.com/astro/node-expat
    category: security
    technology:
    - express
    cwe2022-top25: true
    cwe2021-top25: true
    subcategory:
    - vuln
    likelihood: MEDIUM
    impact: MEDIUM
    confidence: MEDIUM
  languages:
  - javascript
  - typescript
  severity: ERROR
  mode: taint
  pattern-sources:
  - patterns:
    - pattern-either:
      - pattern-inside: function ... ($REQ, $RES) {...}
      - pattern-inside: function ... ($REQ, $RES, $NEXT) {...}
      - patterns:
        - pattern-either:
          - pattern-inside: $APP.$METHOD(..., function $FUNC($REQ, $RES) {...})
          - pattern-inside: $APP.$METHOD(..., function $FUNC($REQ, $RES, $NEXT) {...})
        - metavariable-regex:
            metavariable: $METHOD
            regex: ^(get|post|put|head|delete|options)$
    - pattern-either:
      - pattern: $REQ.query
      - pattern: $REQ.body
      - pattern: $REQ.params
      - pattern: $REQ.cookies
      - pattern: $REQ.headers
  - patterns:
    - pattern-either:
      - pattern-inside: |
          ({ $REQ }: Request,$RES: Response, $NEXT: NextFunction) =>
          {...}
      - pattern-inside: |
          ({ $REQ }: Request,$RES: Response) => {...}
    - focus-metavariable: $REQ
    - pattern-either:
      - pattern: params
      - pattern: query
      - pattern: cookies
      - pattern: headers
      - pattern: body
  pattern-sinks:
  - patterns:
    - pattern-either:
      - pattern-inside: |
          $XML = require('node-expat')
          ...
      - pattern-inside: |
          import $XML from 'node-expat'
          ...
      - pattern-inside: |
          import * as $XML from 'node-expat'
          ...
    - pattern-either:
      - pattern-inside: |
          $PARSER = new $XML.Parser(...);
          ...
    - pattern-either:
      - pattern: $PARSER.parse($QUERY)
      - pattern: $PARSER.write($QUERY)
    - focus-metavariable: $QUERY