Essential Security Headers for Apache

Implementing security headers in Apache requires enabling the headers module and carefully configuring each header. Start by ensuring the module is active:

sudo a2enmod headers
sudo systemctl restart apache2

Configure comprehensive security headers in your Apache virtual host or global configuration:

<IfModule mod_headers.c>
    # Strict Transport Security - Enforce HTTPS
    Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"
    
    # X-Frame-Options - Prevent clickjacking
    Header always set X-Frame-Options "SAMEORIGIN"
    
    # X-Content-Type-Options - Prevent MIME type sniffing
    Header always set X-Content-Type-Options "nosniff"
    
    # X-XSS-Protection - Enable XSS filtering (legacy but still useful)
    Header always set X-XSS-Protection "1; mode=block"
    
    # Referrer-Policy - Control referrer information
    Header always set Referrer-Policy "strict-origin-when-cross-origin"
    
    # Content Security Policy - Comprehensive XSS and injection protection
    Header always set Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval' https://cdn.example.com; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com; img-src 'self' data: https:; connect-src 'self' https://api.example.com; frame-ancestors 'self'; base-uri 'self'; form-action 'self'; upgrade-insecure-requests;"
    
    # Permissions Policy (formerly Feature Policy)
    Header always set Permissions-Policy "geolocation=(), microphone=(), camera=(), payment=(), usb=(), magnetometer=(), accelerometer=(), gyroscope=()"
    
    # X-Permitted-Cross-Domain-Policies - Control cross-domain content handling
    Header always set X-Permitted-Cross-Domain-Policies "none"
    
    # Clear-Site-Data - Clear browsing data on logout
    <Location /logout>
        Header always set Clear-Site-Data '"cache", "cookies", "storage"'
    </Location>
    
    # Remove potentially dangerous headers
    Header always unset X-Powered-By
    Header always unset Server
    
    # Cache-Control for security-sensitive content
    <FilesMatch "\.(html|php)$">
        Header set Cache-Control "no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0"
        Header set Pragma "no-cache"
        Header set Expires "0"
    </FilesMatch>
</IfModule>