XSS

Cross Site Scripting (XSS) is a web security vulnerability allowing attackers to execute malicious scripts in user browsers, potentially compromising sensitive data and interactions.

Types of XSS

1. Reflected XSS:
   • User input immediately returned in web application responses without sanitization.
   • Typically exploited through error messages or search results.
2. Stored XSS (Persistent):
   • Malicious script stored on a web application’s server (e.g., in comments), executed when accessed by users.
3. DOM-Based XSS:
   • Attack payload executed in the browser by modifying the DOM environment without altering the HTTP response.

Possible Attacks

• Cookie Theft: Access session cookies to hijack accounts.
• Keylogging: Record keystrokes to capture sensitive data.
• Phishing: Embed fake forms to steal credentials.

Countermeasures

1. Encoding:
   • Escape user input to prevent browsers from interpreting it as code (e.g., replacing < with <).
2. Validation:
   • Filter malicious input using blacklisting or whitelisting techniques.
3. Input Handling Contexts:
   • Ensure user input is processed securely in all contexts (HTML, attributes, JavaScript).
4. Secure Input Handling:
   • Perform sanitization both server-side (to protect against XSS) and client-side (to protect against DOM-based XSS).