CVE-2021-26106
📋 TL;DR
This vulnerability allows authenticated attackers to execute arbitrary operating system commands on FortiAP devices by exploiting improper input sanitization in the kdbg CLI command. Attackers with valid credentials can run unauthorized commands with elevated privileges. Affected systems include FortiAP running vulnerable firmware versions.
💻 Affected Systems
- FortiAP
📦 What is this software?
Fortiap by Fortinet
Fortiap S by Fortinet
Fortiap W2 by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Full device compromise allowing attacker to install persistent backdoors, pivot to internal networks, exfiltrate sensitive data, or disrupt network operations.
Likely Case
Unauthorized command execution leading to configuration changes, credential theft, or lateral movement within the network.
If Mitigated
Limited impact due to network segmentation, strong authentication controls, and monitoring preventing successful exploitation.
🎯 Exploit Status
Exploitation requires authenticated CLI access and knowledge of the vulnerable kdbg command with crafted arguments.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiAP 6.4.6 and 6.2.6 or later
Vendor Advisory: https://fortiguard.com/advisory/FG-IR-20-210
Restart Required: Yes
Instructions:
1. Download latest firmware from Fortinet support portal. 2. Backup current configuration. 3. Upload and install firmware update via web interface or CLI. 4. Reboot device. 5. Verify version with 'get system status' command.
🔧 Temporary Workarounds
Restrict CLI Access
allLimit administrative access to FortiAP CLI to trusted users only using role-based access controls.
config system admin
edit <username>
set accprofile "prof_admin"
set password <password>
end
Disable Unnecessary CLI Commands
allRemove or restrict access to the kdbg command if not required for operations.
config system console
set output standard
end
🧯 If You Can't Patch
- Implement strict network segmentation to isolate FortiAP management interfaces from untrusted networks.
- Enforce strong authentication policies and monitor for unusual CLI command usage patterns.
🔍 How to Verify
Check if Vulnerable:
Check firmware version with 'get system status' command. If version is between 6.4.1-6.4.5 or 6.2.4-6.2.5, device is vulnerable.Check Version:
get system status | grep VersionVerify Fix Applied:
After patching, verify version is 6.4.6+ or 6.2.6+ using 'get system status' command.📡 Detection & Monitoring
Log Indicators:
- Unusual kdbg command usage patterns
- Multiple failed authentication attempts followed by successful login
- Execution of unexpected system commands
Network Indicators:
- Unusual outbound connections from FortiAP devices
- Traffic patterns inconsistent with normal operations
SIEM Query:
source="fortiap" AND (command="kdbg" OR command="execute" OR command="shell")