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Just discovered a critical Account Takeover (ATO) vulnerability stemming from a misconfigured invitation flow. The attack began by inviting a user (using an attacker-controlled email), receiving the invitation link, and then modifying the email to the victim’s address. Surprisingly, the original link remained valid—allowing the attacker to accept the invitation on behalf of the victim, redirecting to the login page.
Further exploitation revealed a zero-click ATO: when the same invitation link was accessed from a browser already logged into the attacker’s organization, the system directly logged the attacker into the victim’s account without requiring interaction.
You Should Know:
1. Testing for Invitation Flow Vulnerabilities
- Replay Invitation Links: Capture the invitation link via proxy (Burp Suite) and replay it after modifying the email parameter.
curl -X GET "https://target.com/invite?token=ATTACKER_TOKEN&[email protected]"
- Session Validation Check: Verify if the system validates session cookies against the invited email.
hydra -l [email protected] -p password123 target.com http-post-form "/login:email=^USER^&pass=^PASS^:Invalid"
2. Exploiting Misconfigured JWT/Token Validation
- Tamper with JWT Tokens: Use `jwt_tool` to manipulate tokens.
python3 jwt_tool.py <JWT_TOKEN> -T -X a
- Brute-force Weak Tokens:
hashcat -m 16500 jwt_hash.txt rockyou.txt
3. Preventing ATO in Your Applications
- Enforce One-Time Use Tokens:
UPDATE invitations SET used=1 WHERE token='USED_TOKEN';
- Implement Strict Email-Session Binding:
if (session.email !== invited_email) { invalidateToken(); } - Rate-Limit Invitation Endpoints:
limit_req_zone $binary_remote_addr zone=invite_limit:10m rate=5r/m;
4. Post-Exploitation Detection
- Check Suspicious Logins:
grep "failed|success" /var/log/auth.log | awk '{print $1,$6,$9}' - Audit User Sessions:
last -i | grep -E '([0-9]{1,3}.){3}[0-9]{1,3}'
What Undercode Say:
This vulnerability underscores the importance of secure invitation workflows. Key takeaways:
1. Token Binding: Always bind tokens to the original recipient’s email/session.
2. Zero-Click Threats: Assume attackers will chain low-severity bugs (e.g., invitation misuse) into critical exploits.
3. Logging: Log all invitation attempts and session switches for forensic analysis.
Linux Command for Log Analysis:
awk '/Invalid user/ {print $8}' /var/log/auth.log | sort | uniq -c | sort -nr
Windows Command for Session Auditing:
Get-EventLog -LogName Security -InstanceId 4624 -After (Get-Date).AddHours(-1) | Select-Object -Property TimeGenerated,Message
Expected Output:
A detailed report of exploited invitation flows, including:
- Modified HTTP requests.
- Session hijacking evidence.
- Mitigation steps (e.g., token expiration, email validation).
References:
Reported By: Mohamed Kamal – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
