---name: security-headers-configurationdescription: 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
• 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