X-XSS-Protection is a security header that helps protect websites from Cross-Site Scripting (XSS) attacks. When enabled in your web server configuration, it instructs browsers to activate their built-in XSS filters, providing an additional layer of defense against malicious scripts.

This header works by detecting and blocking certain types of reflected XSS attacks—where attackers inject scripts into web pages through user input (like form fields or URL parameters). The browser analyzes pages before rendering them and neutralizes suspicious scripts when the protection is triggered.

Common X-XSS-Protection values include:

• 0 – Disables the filter completely
• 1 – Enables protection and sanitizes the page if an attack is detected
• 1; mode=block – Recommended setting: enables protection and blocks the page entirely instead of sanitizing

While modern browsers are gradually deprecating this header in favor of Content Security Policy (CSP), it remains valuable for older browser support. To implement it, add the header through your server configuration (like .htaccess for Apache or server blocks for Nginx) with the value 1; mode=block for maximum security.

Remember that X-XSS-Protection is just one part of a comprehensive security strategy. Always combine it with other measures like CSP, input validation, and regular security updates to keep your hosting environment secure.