---

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.

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
• Mozilla Observatory
• CSP Evaluator

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 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