CVE-2021-20140
📋 TL;DR
An unauthenticated command injection vulnerability in Gryphon Tower routers allows attackers on the same network to execute arbitrary commands as root. This affects Gryphon Tower routers with the vulnerable controller_server service running on port 9999. Attackers can gain complete control of the device without authentication.
💻 Affected Systems
- Gryphon Tower routers
📦 What is this software?
Gryphon Tower Firmware by Gryphonconnect
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of router with root access, enabling network traffic interception, credential theft, lateral movement to other devices, and persistent backdoor installation.
Likely Case
Router takeover leading to DNS hijacking, credential harvesting, and use as pivot point for attacking other devices on the network.
If Mitigated
Limited impact if network segmentation isolates routers from untrusted devices and proper access controls are implemented.
🎯 Exploit Status
Exploitation requires network access to port 9999, which is typically only accessible on local network
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware updates released by Gryphon to address this vulnerability
Vendor Advisory: https://www.tenable.com/security/research/tra-2021-51
Restart Required: Yes
Instructions:
1. Log into Gryphon router admin interface
2. Navigate to firmware update section
3. Check for and apply latest firmware
4. Reboot router after update completes
🔧 Temporary Workarounds
Block port 9999 at network perimeter
linuxPrevent external access to vulnerable service by blocking port 9999 at firewall
iptables -A INPUT -p tcp --dport 9999 -j DROP
Disable controller_server service
linuxStop and disable the vulnerable service if not required
systemctl stop controller_server
systemctl disable controller_server
🧯 If You Can't Patch
- Segment router on isolated network VLAN to limit attack surface
- Implement strict network access controls to restrict access to port 9999
🔍 How to Verify
Check if Vulnerable:
Check if controller_server service is listening on port 9999: netstat -tlnp | grep 9999Check Version:
Check router admin interface for firmware version or use vendor-specific CLI commandsVerify Fix Applied:
Verify service is no longer vulnerable by checking firmware version and testing with known exploit📡 Detection & Monitoring
Log Indicators:
- Unusual connections to port 9999
- Suspicious command execution in system logs
- Unexpected process creation
Network Indicators:
- Malformed packets to port 9999
- Command injection patterns in network traffic
SIEM Query:
source_port:9999 AND (payload_contains:"||" OR payload_contains:";" OR payload_contains:"$")