xss-prevention
Prevent Cross-Site Scripting (XSS) attacks through input sanitization, output encoding, and Content Security Policy. Use when handling user-generated content in web applications.
What this skill does
# XSS Prevention
## Table of Contents
- [Overview](#overview)
- [When to Use](#when-to-use)
- [Quick Start](#quick-start)
- [Reference Guides](#reference-guides)
- [Best Practices](#best-practices)
## Overview
Implement comprehensive Cross-Site Scripting (XSS) prevention using input sanitization, output encoding, CSP headers, and secure coding practices.
## When to Use
- User-generated content display
- Rich text editors
- Comment systems
- Search functionality
- Dynamic HTML generation
- Template rendering
## Quick Start
Minimal working example:
```javascript
// xss-prevention.js
const createDOMPurify = require("dompurify");
const { JSDOM } = require("jsdom");
const he = require("he");
const window = new JSDOM("").window;
const DOMPurify = createDOMPurify(window);
class XSSPrevention {
/**
* HTML Entity Encoding - Safest for text content
*/
static encodeHTML(str) {
return he.encode(str, {
useNamedReferences: true,
encodeEverything: false,
});
}
/**
* Sanitize HTML - For rich content
*/
static sanitizeHTML(dirty) {
const config = {
ALLOWED_TAGS: [
// ... (see reference guides for full implementation)
```
## Reference Guides
Detailed implementations in the `references/` directory:
| Guide | Contents |
|---|---|
| [Node.js XSS Prevention](references/nodejs-xss-prevention.md) | Node.js XSS Prevention |
| [Python XSS Prevention](references/python-xss-prevention.md) | Python XSS Prevention |
| [React XSS Prevention](references/react-xss-prevention.md) | React XSS Prevention |
| [Content Security Policy](references/content-security-policy.md) | Content Security Policy |
## Best Practices
### ✅ DO
- Encode output by default
- Use templating engines
- Implement CSP headers
- Sanitize rich content
- Validate URLs
- Use HTTPOnly cookies
- Regular security testing
- Use secure frameworks
### ❌ DON'T
- Trust user input
- Use innerHTML directly
- Skip output encoding
- Allow inline scripts
- Use eval()
- Mix contexts (HTML/JS)
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