How to Test for Cross-Site Scripting (XSS) Vulnerabilities

📚 Quick Study Guide

• 🔍 What is XSS? XSS vulnerabilities allow attackers to inject malicious scripts into websites viewed by other users.
• 🛡️ Types of XSS:
  • Stored XSS: Script is permanently stored on the target server (e.g., in a database).
  • Reflected XSS: Script is injected through a request and immediately reflected back to the user.
  • DOM-based XSS: Vulnerability exists in the client-side code rather than the server-side code.
• 🧪 Testing Techniques:
  • Manual Testing: Inputting common XSS payloads in every input field.
  • Automated Scanners: Using tools like OWASP ZAP or Burp Suite to automatically detect vulnerabilities.
• 💡 Common Payloads:
  • <script>alert('XSS')</script>
  • <img src=x onerror=alert('XSS')>
• 📝 Prevention:
  • Input Validation: Sanitize user inputs to remove or encode potentially malicious code.
  • Output Encoding: Encode data before displaying it on a web page.
  • Content Security Policy (CSP): Configure CSP headers to restrict the sources from which scripts can be loaded.

Practice Quiz

1. Which type of XSS involves storing the malicious script on the server?
   1. Reflected XSS
   2. Stored XSS
   3. DOM-based XSS
   4. Blind XSS
2. What is a common XSS payload used for testing?
   1. <div>
   2. <script>alert('XSS')</script>
   3. <p>
   4. <h1>
3. Which XSS type manipulates the client-side DOM?
   1. Stored XSS
   2. Reflected XSS
   3. DOM-based XSS
   4. Server-side XSS
4. What is a primary method to prevent XSS?
   1. Disable JavaScript
   2. Input Validation
   3. Disable Cookies
   4. Block all user input
5. What security measure involves setting HTTP headers to control script sources?
   1. Cross-Origin Resource Sharing (CORS)
   2. Content Security Policy (CSP)
   3. HTTP Strict Transport Security (HSTS)
   4. Same-Origin Policy (SOP)
6. Which tool can be used for automated XSS vulnerability scanning?
   1. Wireshark
   2. Nmap
   3. OWASP ZAP
   4. tcpdump
7. What is the purpose of output encoding in XSS prevention?
   1. To encrypt the entire webpage
   2. To modify data before displaying it to prevent malicious code execution
   3. To compress data for faster loading
   4. To hide data from users