CVE-2020-12812
📋 TL;DR
This vulnerability allows attackers to bypass two-factor authentication in FortiOS SSL VPN by changing the case of their username. Attackers can gain unauthorized access to VPN-protected networks without providing the required second authentication factor. Organizations using affected FortiOS versions with SSL VPN and FortiToken authentication are at risk.
💻 Affected Systems
- FortiOS
📦 What is this software?
Fortios by Fortinet
Fortios by Fortinet
Fortios by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Complete network compromise through unauthorized VPN access, leading to data exfiltration, lateral movement, and ransomware deployment.
Likely Case
Unauthorized access to internal resources, credential theft, and potential data breaches.
If Mitigated
Limited impact if VPN access is restricted to specific resources and monitored for unusual login patterns.
🎯 Exploit Status
Exploitation requires valid username credentials but bypasses second factor. CISA lists this as known exploited.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiOS 6.4.1, 6.2.4, 6.0.10 and later
Vendor Advisory: https://fortiguard.com/psirt/FG-IR-19-283
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Download appropriate firmware version from Fortinet support portal. 3. Upload firmware to FortiGate device. 4. Install firmware update. 5. Reboot device. 6. Verify version and test VPN functionality.
🔧 Temporary Workarounds
Disable SSL VPN
allTemporarily disable SSL VPN access until patching can be completed.
config vpn ssl settings
set status disable
end
Enforce username case sensitivity
allConfigure authentication to treat usernames as case-sensitive.
config user local
edit <username>
set case-sensitivity enable
end
🧯 If You Can't Patch
- Implement network segmentation to limit VPN access to only necessary resources
- Enable detailed logging and monitoring for VPN authentication attempts, especially case variations
🔍 How to Verify
Check if Vulnerable:
Check FortiOS version via CLI: get system status | grep Version. If version matches affected range and SSL VPN with FortiToken is enabled, system is vulnerable.Check Version:
get system status | grep VersionVerify Fix Applied:
Verify version is patched: get system status | grep Version. Test authentication with case-varied username to confirm 2FA prompt appears.📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts with case-varied usernames
- Successful logins without 2FA token validation
- Login attempts with username case modifications
Network Indicators:
- Unusual VPN connection patterns from unexpected locations
- VPN traffic spikes during non-business hours
SIEM Query:
source="fortigate" AND (event="user authentication" AND NOT token_used="yes") OR (username MATCHES "[a-zA-Z]+" AND LOWER(username) IN known_users)