CVE-2021-4039
📋 TL;DR
This CVE-2021-4039 is a command injection vulnerability in Zyxel NWA-1100-NH access point web interface that allows authenticated attackers to execute arbitrary operating system commands on the device. It affects organizations using these specific Zyxel access points with vulnerable firmware versions. The high CVSS score of 9.8 indicates critical severity.
💻 Affected Systems
- Zyxel NWA-1100-NH Wireless Access Point
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to install persistent backdoors, pivot to internal networks, intercept traffic, or brick the device.
Likely Case
Attacker gains full control of the access point, enabling network traffic interception, credential theft, and lateral movement within the network.
If Mitigated
Limited impact if device is isolated, properly segmented, and monitored with intrusion detection.
🎯 Exploit Status
Public exploit code available on Packet Storm. Requires authentication but exploitation is straightforward once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V6.10(ABYW.1)C0 or later
Vendor Advisory: https://www.zyxel.com/support/OS-command-injection-vulnerability-of-NWA1100-NH-access-point.shtml
Restart Required: Yes
Instructions:
1. Download latest firmware from Zyxel support portal. 2. Log into web interface. 3. Navigate to Maintenance > Firmware Upgrade. 4. Upload firmware file. 5. Apply and wait for reboot.
🔧 Temporary Workarounds
Network Segmentation
allIsolate access point management interface from untrusted networks
Access Control
allRestrict web interface access to trusted IP addresses only
🧯 If You Can't Patch
- Disable web interface and manage via console if possible
- Implement strict network segmentation and firewall rules to limit access to management interface
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface: System Info > Firmware VersionCheck Version:
Not applicable - check via web interface or consoleVerify Fix Applied:
Verify firmware version is V6.10(ABYW.1)C0 or later in System Info📡 Detection & Monitoring
Log Indicators:
- Unusual command execution in system logs
- Multiple failed login attempts followed by successful login and command execution
- Unexpected system processes or services
Network Indicators:
- Unusual outbound connections from access point
- Traffic patterns inconsistent with normal AP operation
- Management interface accessed from unusual IPs
SIEM Query:
source="zyxel-nwa1100" AND (event_type="command_execution" OR process="unusual_process")🔗 References
- http://packetstormsecurity.com/files/166752/Zyxel-NWA-1100-NH-Command-Injection.html
- https://www.zyxel.com/support/OS-command-injection-vulnerability-of-NWA1100-NH-access-point.shtml
- http://packetstormsecurity.com/files/166752/Zyxel-NWA-1100-NH-Command-Injection.html
- https://www.zyxel.com/support/OS-command-injection-vulnerability-of-NWA1100-NH-access-point.shtml
