Security headers instruct browsers to enable protective features. Content Security Policy prevents XSS by controlling resource loading. HSTS enforces HTTPS connections. X-Frame-Options blocks clickjacking attacks. Proper configuration provides significant protection with minimal implementation effort.
Essential Headers
Content-Security-Policy controls which resources can load, blocking inline scripts and unauthorized sources. Strict-Transport-Security enforces HTTPS for specified duration. X-Content-Type-Options prevents MIME-type sniffing. X-Frame-Options controls iframe embedding.
- Start with report-only CSP to identify violations before enforcement
- Set HSTS with appropriate max-age—longer is more secure but harder to undo
- Use X-Content-Type-Options: nosniff universally
- Configure X-Frame-Options based on iframe embedding requirements
- Add Permissions-Policy to disable unnecessary browser features
Implementation Strategy
Implement headers at reverse proxy or CDN level for consistent application. Start with permissive policies and tighten iteratively. Monitor CSP violations to catch legitimate resources blocked by policy. Test thoroughly—overly strict policies break functionality.