mcp-server-semgrep/semgrep-rules/javascript/express/security/audit/xss/direct-response-write.yaml

MCP Server for Semgrep Integration - static code analysis with AI

rules:
- id: direct-response-write
  message: >-
    Detected directly writing to a Response object from user-defined input.
    This bypasses any HTML escaping and may expose your application to a Cross-Site-scripting
    (XSS) vulnerability. Instead, use 'resp.render()' to render safely escaped HTML.
  options:
    interfile: true
  metadata:
    interfile: true
    references:
    - https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html
    owasp:
    - A07:2017 - Cross-Site Scripting (XSS)
    - A03:2021 - Injection
    cwe:
    - 'CWE-79: Improper Neutralization of Input During Web Page Generation (''Cross-site
      Scripting'')'
    category: security
    technology:
    - express
    cwe2022-top25: true
    cwe2021-top25: true
    subcategory:
    - vuln
    likelihood: MEDIUM
    impact: MEDIUM
    confidence: MEDIUM
    vulnerability_class:
    - Cross-Site-Scripting (XSS)
  languages:
  - javascript
  - typescript
  severity: WARNING
  mode: taint
  pattern-sources:
  - patterns:
    - pattern-either:
      - pattern-inside: function ... ($REQ, $RES) {...}
      - pattern-inside: function ... ($REQ, $RES, $NEXT) {...}
      - patterns:
        - pattern-inside: $APP.$METHOD(..., function $FUNC($REQ, $RES) {...})
        - metavariable-regex:
            metavariable: $METHOD
            regex: ^(get|post|put|head|delete|options)
    - pattern-not-inside: |
        function ... ($REQ, $RES) {
            ...
            $RES.$SET('Content-Type', '$TYPE')
        }
    - pattern-not-inside: |
        $APP.$METHOD(..., function $FUNC($REQ, $RES) {
            ...
            $RES.$SET('Content-Type', '$TYPE')
        })
    - pattern-not-inside: |
        function ... ($REQ, $RES, $NEXT) {
            ...
            $RES.$SET('Content-Type', '$TYPE')
        }
    - pattern-not-inside: |
        function ... ($REQ, $RES) {
            ...
            $RES.set('$TYPE')
        }
    - pattern-not-inside: |
        $APP.$METHOD(..., function $FUNC($REQ, $RES) {
            ...
            $RES.set('$TYPE')
        })
    - pattern-not-inside: |
        function ... ($REQ, $RES, $NEXT) {
            ...
            $RES.set('$TYPE')
        }
    - pattern-either:
      - pattern: $REQ.query
      - pattern: $REQ.body
      - pattern: $REQ.params
  - patterns:
    - pattern-either:
      - pattern-inside: |
          ({ $REQ }: Request,$RES: Response, $NEXT: NextFunction) =>
          {...}
      - pattern-inside: |
          ({ $REQ }: Request,$RES: Response) => {...}
    - pattern-not-inside: |
        ({ $REQ }: Request,$RES: Response, $NEXT: NextFunction) =>
        {
            ...
            $RES.$SET('Content-Type', '$TYPE')
        }
    - pattern-not-inside: |
        ({ $REQ }: Request,$RES: Response) => {
            ...
            $RES.$SET('Content-Type', '$TYPE')
        }
    - pattern-not-inside: |
        ({ $REQ }: Request,$RES: Response, $NEXT: NextFunction) =>
        {
            ...
            $RES.set('$TYPE')
        }
    - focus-metavariable: $REQ
    - pattern-either:
      - pattern: params
      - pattern: query
      - pattern: body
  pattern-sinks:
  - patterns:
    - pattern-inside: function ... (..., $RES,...) {...}
    - pattern-either:
      - pattern: $RES.write($ARG)
      - pattern: $RES.send($ARG)
    - pattern-not: $RES. ... .set('...'). ... .send($ARG)
    - pattern-not: $RES. ... .type('...'). ... .send($ARG)
    - pattern-not-inside: $RES.$METHOD({ ... })
    - focus-metavariable: $ARG
  pattern-sanitizers:
  - patterns:
    - pattern-either:
      - pattern-inside: |
          import $S from "underscore.string"
          ...
      - pattern-inside: |
          import * as $S from "underscore.string"
          ...
      - pattern-inside: |
          import $S from "underscore.string"
          ...
      - pattern-inside: |
          $S = require("underscore.string")
          ...
    - pattern-either:
      - pattern: $S.escapeHTML(...)
  - patterns:
    - pattern-either:
      - pattern-inside: |
          import $S from "dompurify"
          ...
      - pattern-inside: |
          import { ..., $S,... } from "dompurify"
          ...
      - pattern-inside: |
          import * as $S from "dompurify"
          ...
      - pattern-inside: |
          $S = require("dompurify")
          ...
      - pattern-inside: |
          import $S from "isomorphic-dompurify"
          ...
      - pattern-inside: |
          import * as $S from "isomorphic-dompurify"
          ...
      - pattern-inside: |
          $S = require("isomorphic-dompurify")
          ...
    - pattern-either:
      - patterns:
        - pattern-inside: |
            $VALUE = $S(...)
            ...
        - pattern: $VALUE.sanitize(...)
      - patterns:
        - pattern-inside: |
            $VALUE = $S.sanitize
            ...
        - pattern: $S(...)
      - pattern: $S.sanitize(...)
      - pattern: $S(...)
  - patterns:
    - pattern-either:
      - pattern-inside: |
          import $S from 'xss';
          ...
      - pattern-inside: |
          import * as $S from 'xss';
          ...
      - pattern-inside: |
          $S = require("xss")
          ...
    - pattern: $S(...)
  - patterns:
    - pattern-either:
      - pattern-inside: |
          import $S from 'sanitize-html';
          ...
      - pattern-inside: |
          import * as $S from "sanitize-html";
          ...
      - pattern-inside: |
          $S = require("sanitize-html")
          ...
    - pattern: $S(...)
  - patterns:
    - pattern-either:
      - pattern-inside: |
          $S = new Remarkable()
          ...
    - pattern: $S.render(...)
  - patterns:
    - pattern-either:
      - pattern-inside: |
          import $S from 'express-xss-sanitizer';
          ...
      - pattern-inside: |
          import * as $S from "express-xss-sanitizer";
          ...
      - pattern-inside: |
          const { ..., $S, ... } = require('express-xss-sanitizer');
          ...
      - pattern-inside: |
          var { ..., $S, ... } = require('express-xss-sanitizer');
          ...
      - pattern-inside: |
          let { ...,$S,... } = require('express-xss-sanitizer');
          ...
      - pattern-inside: |
          $S = require("express-xss-sanitizer")
          ...
    - pattern: $S(...)
  - patterns:
    - pattern: $RES. ... .type('$F'). ... .send(...)
    - metavariable-regex:
        metavariable: $F
        regex: (?!.*text/html)
  - patterns:
    - pattern-inside: |
        $X = [...];
        ...
    - pattern: |
        if(<... !$X.includes($SOURCE)...>) {
            ...
            return ...
        }
        ...
    - pattern: $SOURCE