/security-headers-configuration

name: security-headers-configuration
description: Configures HTTP security headers to protect against XSS, clickjacking, and MIME sniffing attacks. Use when hardening web applications, passing security audits, or implementing Content Security Policy.
license: MIT

Security Headers Configuration

Implement HTTP security headers to defend against common browser-based attacks.

Essential Headers

| Header | Purpose | Value | |--------|---------|-------| | HSTS | Force HTTPS | `max-age=31536000; includeSubDomains` | | CSP | Restrict resources | `default-src 'self'` | | X-Frame-Options | Prevent clickjacking | `DENY` | | X-Content-Type-Options | Prevent MIME sniffing | `nosniff` |

Express Implementation

const helmet = require('helmet');

app.use(helmet());

// Custom CSP
app.use(helmet.contentSecurityPolicy({
  directives: {
    defaultSrc: ["'self'"],
    scriptSrc: ["'self'", "'unsafe-inline'"],
    styleSrc: ["'self'", "'unsafe-inline'"],
    imgSrc: ["'self'", "data:", "https:"],
    connectSrc: ["'self'", "https://api.example.com"],
    fontSrc: ["'self'", "https://fonts.gstatic.com"],
    frameAncestors: ["'none'"]
  }
}));

Nginx Configuration

add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;
add_header X-Frame-Options "DENY" always;
add_header X-Content-Type-Options "nosniff" always;
add_header X-XSS-Protection "1; mode=block" always;
add_header Referrer-Policy "strict-origin-when-cross-origin" always;
add_header Permissions-Policy "geolocation=(), microphone=(), camera=()" always;
add_header Content-Security-Policy "default-src 'self'; script-src 'self'" always;

Verification Tools

• [Security Headers](https://securityheaders.com/)
• [Mozilla Observatory](https://observatory.mozilla.org/)
• [CSP Evaluator](https://csp-evaluator.withgoogle.com/)

Security Headers Checklist

• [ ] HSTS enabled with long max-age
• [ ] CSP configured and tested
• [ ] X-Frame-Options set to DENY
• [ ] X-Content-Type-Options set to nosniff
• [ ] Referrer-Policy configured
• [ ] Permissions-Policy disables unused features

Additional Implementations

See [references/python-apache.md](references/python-apache.md) for:

• Python Flask security headers middleware
• Flask-Talisman library configuration
• Apache .htaccess configuration
• Header testing script

Common Mistakes

• Setting CSP to report-only permanently
• Using overly permissive policies
• Forgetting to test after changes
• Not including all subdomains in HSTS