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Cross-Site Scripting (XSS) remains a critical web vulnerability, allowing attackers to inject malicious scripts into trusted websites. In this case, a $300 bounty was awarded for discovering an XSS flaw. Below, we dive into XSS exploitation techniques, verification, and mitigation.
You Should Know:
1. Types of XSS
- Stored XSS: Malicious script is permanently stored on the target server.
- Reflected XSS: The script is reflected off a web server (e.g., via URL parameters).
- DOM-based XSS: The vulnerability exists in client-side code rather than server-side.
2. Basic XSS Payloads
<script>alert('XSS')</script>
<img src=x onerror=alert(1)>
<
svg/onload=alert(1)>
3. Advanced Exploitation (Bypassing Filters)
< iframe src="javascript:alert(<code>XSS</code>)"> <a href="data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4=">Click</a>
4. Testing for XSS
- Use Burp Suite or OWASP ZAP to intercept and modify requests.
- Automated tools:
nikto -h target.com -Tuning 4 xsstrike -u "http://target.com/search?q=test"
5. Mitigation Techniques
- Input Sanitization: Use libraries like DOMPurify.
- Content Security Policy (CSP):
Content-Security-Policy: default-src 'self'; script-src 'unsafe-inline' 'unsafe-eval';
- HTTP-only Cookies: Prevent JavaScript access.
6. Linux Commands for XSS Testing
curl -X POST "http://target.com/search" --data "q=<script>alert(1)</script>" grep -r "echo $_GET" /var/www/html Find potential XSS in PHP code
7. Windows Command for XSS Detection
Invoke-WebRequest -Uri "http://target.com?param=<script>alert(1)</script>"
What Undercode Say
XSS remains a top web security threat due to improper input handling. Always sanitize user inputs, enforce CSP, and conduct regular penetration testing. Bug bounty programs incentivize researchers to uncover flaws before malicious actors do.
Prediction
As web applications grow more complex, DOM-based XSS and API-related XSS will rise. Automation in bug hunting will increase, but manual testing will remain crucial for advanced exploits.
Expected Output:
A secure web application with proper input validation, CSP headers, and regular security audits to prevent XSS attacks.
Relevant URLs:
(Note: Since no specific URL was provided in the original post, general XSS resources are included.)
References:
Reported By: Shivangmauryaa Bounty – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
