TryHackMe: Cross-Site Scripting (XSS) Deep Dive

Understanding XSS

Cross-Site Scripting (XSS) allows attackers to inject malicious scripts into web pages viewed by other users.

Types of XSS

1. Stored (Persistent) XSS

• Malicious script is stored in the database
• Affects all users who view the page
• More dangerous than reflected XSS

2. Reflected XSS

• Malicious script is reflected in the URL
• Requires user interaction (clicking a link)
• Affects only that user

3. DOM-based XSS

• Vulnerability exists in client-side code
• JavaScript processes user input unsafely

Real-world Impact

• Session hijacking
• Credential theft
• Malware distribution
• Defacement

Mitigation Strategies

1. Input validation and sanitization
2. Output encoding
3. Content Security Policy (CSP)
4. HTTPOnly and Secure flags on cookies
5. Regular security testing

Testing for XSS

<script>alert('XSS Vulnerability')</script>
<img src=x onerror="alert('XSS')">
<svg onload="alert('XSS')">