How to Prevent Cross-Site Scripting (XSS) Attacks

Cross-site scripting (XSS) is an attack where malicious JavaScript is injected into web pages viewed by other users. When a visitor loads an infected page, the script runs in their browser - potentially stealing session cookies, redirecting them to phishing sites, or capturing keystrokes.

Types of XSS Attacks

• Stored XSS: Malicious script is saved in the database (e.g., via a comment form) and executed every time the page loads.
• Reflected XSS: The script is embedded in a URL parameter and only executes when the victim clicks a specially crafted link.
• DOM-based XSS: The attack manipulates the page's DOM through client-side JavaScript without involving the server.

Developer-Level Defences

• Escape output: Always escape user-supplied data before rendering it in HTML. Use your language's built-in escaping functions (e.g., htmlspecialchars() in PHP).
• Content Security Policy (CSP): Add a Content-Security-Policy HTTP header to restrict which scripts can run on your pages.
• Validate and sanitize input: Never trust data from users - strip or encode special characters like <, >, and &.
• Use HTTPOnly cookies: Mark session cookies as HttpOnly so they can't be accessed by JavaScript.

Server & CMS Level

• Enable ModSecurity in cPanel - its ruleset includes XSS detection patterns.
• Keep WordPress and all plugins updated - many XSS vulnerabilities are patched in updates.
• Use a security plugin like Wordfence that includes XSS protection in its firewall.

Need help hardening your site against XSS? Contact our support team.