CVE-2021-26108
📋 TL;DR
This vulnerability involves hard-coded cryptographic keys in FortiOS SSLVPN that could be extracted through reverse engineering. Attackers could potentially decrypt VPN traffic or impersonate legitimate VPN connections. Organizations using affected FortiOS versions with SSLVPN enabled are at risk.
💻 Affected Systems
- FortiOS
📦 What is this software?
Fortios by Fortinet
Fortios by Fortinet
Fortios by Fortinet
Fortios by Fortinet
Fortios by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of VPN communications, allowing attackers to decrypt sensitive traffic, intercept credentials, and establish unauthorized VPN connections to internal networks.
Likely Case
Attackers decrypt VPN sessions to steal credentials and sensitive data, potentially leading to lateral movement within the network.
If Mitigated
Limited impact if VPN traffic contains only non-sensitive data or if additional encryption layers are implemented.
🎯 Exploit Status
Exploitation requires reverse engineering skills to extract keys, but once obtained, the attack becomes straightforward.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 7.0.1 and later
Vendor Advisory: https://fortiguard.com/advisory/FG-IR-21-051
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Download FortiOS 7.0.1 or later from Fortinet support portal. 3. Upload firmware to FortiGate. 4. Install update via CLI or web interface. 5. Reboot device.
🔧 Temporary Workarounds
Disable SSLVPN
allTemporarily disable SSLVPN service if not required
config vpn ssl settings
set status disable
end
Restrict VPN Access
allLimit VPN access to specific IP ranges if possible
config firewall address
edit "VPN_ALLOWED_IPS"
set subnet x.x.x.x y.y.y.y
end
config vpn ssl settings
set source-address "VPN_ALLOWED_IPS"
end
🧯 If You Can't Patch
- Implement network segmentation to isolate VPN traffic
- Deploy additional encryption layer (IPsec tunnel over SSLVPN)
🔍 How to Verify
Check if Vulnerable:
Check FortiOS version via CLI: get system status | grep Version. If version is below 7.0.1 and SSLVPN is enabled, system is vulnerable.Check Version:
get system status | grep VersionVerify Fix Applied:
After patching, verify version is 7.0.1 or higher: get system status | grep Version📡 Detection & Monitoring
Log Indicators:
- Unusual VPN connection patterns
- Multiple failed VPN authentication attempts from same source
- VPN sessions with abnormal duration or data transfer
Network Indicators:
- Unencrypted VPN traffic detection
- Traffic patterns inconsistent with normal VPN usage
SIEM Query:
source="fortigate" (eventtype="vpn" OR eventtype="sslvpn") | stats count by src_ip, user | where count > threshold