This document outlines the security measures implemented in the Mural collaborative pixel art application.

• XSS Prevention: All user-generated content is now rendered using textContent instead of innerHTML
• Coordinate Validation: Strict type checking and bounds validation for pixel placement
• Color Format Validation: Hex color format validation with regex pattern #[0-9A-Fa-f]{6}
• Server-side Validation: All inputs are validated on both client and server sides

• Session Security:
  • Server-side session generation with UUID
  • Session metadata tracking (created_at)
  • HttpOnly, Secure, and SameSite cookie flags
  • Session validation on each request
• Rate Limiting: Implemented per-user rate limiting (60 requests/minute default)
• WebSocket Authentication: WebSocket connections require valid session

• User Privacy: User IDs are hashed (SHA256) before broadcasting to other clients
• Secure Headers: Implemented security headers including CSP, X-Frame-Options, etc.
• HTTPS Enforcement: HSTS header for production environments

• DOM-based XSS Prevention: All dynamic content uses safe DOM manipulation methods
• Content Security Policy: Restrictive CSP that only allows necessary resources
• Safe Event Handlers: Event listeners attached via addEventListener instead of inline handlers

• CORS Configuration: Production uses whitelist of allowed origins
• WebSocket Validation: Connections rejected without valid session
• Large Data Handling: Large canvas data redirected to API endpoint

The following security headers are implemented:

Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-inline' https://cdn.tailwindcss.com https://cdnjs.cloudflare.com; style-src 'self' 'unsafe-inline' https://cdn.tailwindcss.com; font-src 'self' data:; img-src 'self' data: blob:; connect-src 'self' ws: wss:; frame-ancestors 'none';
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
X-XSS-Protection: 1; mode=block
Referrer-Policy: strict-origin-when-cross-origin
Strict-Transport-Security: max-age=31536000; includeSubDomains (production only)

# Required for production
SECRET_KEY=<strong-random-key>
SESSION_COOKIE_SECURE=true
CORS_ORIGINS=https://yourdomain.com,https://anotherdomain.com

# Optional
RATE_LIMIT_PIXELS_PER_MINUTE=10

1. Keep Dependencies Updated: Regularly update Flask, Flask-SocketIO, and other dependencies
2. Environment Separation: Use different configurations for development and production
3. Secret Management: Never commit secrets to version control
4. Regular Audits: Periodically review security measures and update as needed

While comprehensive security measures have been implemented, consider these additional steps:

1. API Authentication: Implement API keys or OAuth for programmatic access
2. DDoS Protection: Use services like Cloudflare for additional protection
3. Database Security: If migrating from JSON to database, implement proper parameterized queries
4. Monitoring: Implement security monitoring and alerting
5. Backup: Regular backups of canvas data

To test the implemented security measures:

1. XSS Testing: Try injecting <script>alert('XSS')</script> in various inputs
2. Rate Limiting: Send rapid requests to test rate limiting
3. Session Security: Try manipulating session cookies
4. CORS: Test cross-origin requests from unauthorized domains