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2025-02-13
During a recent black-box engagement, I discovered a critical vulnerability in a file uploader feature that led to a Stored Cross-Site Scripting (XSS) attack. Here’s a detailed breakdown of the exploit and how it was executed:
Steps to Reproduce the Exploit:
1. Identify the Vulnerable Endpoint:
I found an endpoint that allowed users to upload PDF files. For example, a file named `HowNoobsHack.pdf` could be uploaded.
2. Intercept the Request:
Using BurpSuite, I intercepted the HTTP request during the file upload process. The request contained a `File Name` header.
3. Inject the Payload:
I modified the `File Name` header to include a malicious XSS payload:
File Name: "<script>alert('XSS')</script>.pdf"
4. Execute the Exploit:
After sending the modified request, the payload was executed, resulting in a successful XSS attack.
Practice-Verified Code and Commands:
To replicate this exploit in a controlled environment, you can use the following commands and tools:
- BurpSuite Setup:
Start BurpSuite and configure your browser to route traffic through it. Use the `Proxy` tab to intercept requests. Payload Injection:
Modify the `File Name` header in the intercepted request as shown above.Testing for XSS:
Use the following payloads to test for XSS vulnerabilities:<script>alert('XSS')</script> <img src="x" onerror="alert('XSS')">Linux Command to Monitor Logs:
Use `tail -f /var/log/apache2/access.log` to monitor web server logs for suspicious activity.Windows Command to Check Network Connections:
Use `netstat -an` to check active network connections and identify potential malicious activity.
What Undercode Say:
Cross-Site Scripting (XSS) vulnerabilities remain one of the most common and dangerous security flaws in web applications. This exploit demonstrates how a simple file upload feature can be manipulated to execute malicious scripts, potentially compromising user data and application integrity.
To mitigate such vulnerabilities, developers should implement strict input validation and sanitization. For instance, use libraries like DOMPurify to sanitize user inputs and enforce Content Security Policies (CSP) to restrict the execution of unauthorized scripts.
Additionally, regular security assessments, including penetration testing and code reviews, are essential to identify and remediate vulnerabilities before they can be exploited. Tools like BurpSuite, OWASP ZAP, and Nessus can be invaluable in these efforts.
For further reading on securing web applications, refer to the following resources:
– OWASP XSS Prevention Cheat Sheet
– BurpSuite Documentation
– Linux Command Line for Penetration Testers
By understanding and addressing these vulnerabilities, we can build more secure and resilient web applications. Always remember, ethical hacking is about finding and fixing flaws, not exploiting them for malicious purposes. Stay curious, stay ethical, and keep learning!
References:
Hackers Feeds, Undercode AI
