CVE-2026-22153
📋 TL;DR
This vulnerability allows unauthenticated attackers to bypass LDAP authentication for Agentless VPN or FSSO policies in Fortinet FortiOS when the remote LDAP server is configured in a specific way. It affects FortiOS versions 7.6.0 through 7.6.4. Attackers could potentially gain unauthorized network access without valid credentials.
💻 Affected Systems
- Fortinet FortiOS
📦 What is this software?
Fortios by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Complete network compromise through unauthorized VPN access, lateral movement, data exfiltration, and privilege escalation.
Likely Case
Unauthorized network access through VPN bypass, potentially leading to internal resource access and credential harvesting.
If Mitigated
Limited impact with proper network segmentation, multi-factor authentication, and monitoring in place.
🎯 Exploit Status
Requires specific LDAP server configuration to be exploitable. No public exploit code available at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiOS 7.6.5 or later
Vendor Advisory: https://fortiguard.fortinet.com/psirt/FG-IR-25-1052
Restart Required: Yes
Instructions:
1. Download FortiOS 7.6.5 or later from Fortinet support portal. 2. Backup current configuration. 3. Upload and install the new firmware. 4. Reboot the FortiGate device. 5. Verify the upgrade was successful.
🔧 Temporary Workarounds
Disable vulnerable authentication methods
allTemporarily disable Agentless VPN or FSSO policies using LDAP authentication until patched.
config vpn ssl settings
set tunnel-ip-pools ""
set tunnel-ipv6-pools ""
set source-interface ""
end
Use alternative authentication methods
allSwitch to RADIUS, local authentication, or certificate-based authentication instead of LDAP.
config user group
edit <group_name>
set member <alternative_auth_method>
end
🧯 If You Can't Patch
- Implement network segmentation to isolate VPN traffic and limit lateral movement
- Enable multi-factor authentication for all VPN and network access
🔍 How to Verify
Check if Vulnerable:
Check FortiOS version with 'get system status' and verify if using LDAP authentication for Agentless VPN or FSSO policies.Check Version:
get system status | grep VersionVerify Fix Applied:
Verify FortiOS version is 7.6.5 or later with 'get system status' and test LDAP authentication functionality.📡 Detection & Monitoring
Log Indicators:
- Failed LDAP authentication attempts followed by successful VPN connections
- VPN connections from unexpected IP addresses
- Authentication source changes in logs
Network Indicators:
- Unusual VPN connection patterns
- Traffic from VPN IPs to internal resources not normally accessed
SIEM Query:
source="fortigate" (eventtype="vpn" OR eventtype="authentication") | search "LDAP" AND "success" | stats count by src_ip, user