CVE-2021-20142
📋 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 affected devices 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, allowing network traffic interception, credential theft, malware deployment, and pivot to other internal systems.
Likely Case
Router takeover leading to DNS hijacking, credential harvesting, and persistent backdoor installation for ongoing surveillance.
If Mitigated
Limited impact if network segmentation isolates routers and strict firewall rules block port 9999 access.
🎯 Exploit Status
Exploit requires crafting a malicious packet to port 9999 with command injection in operation 41 parameters. No authentication needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: GryphonOS 4.0.0 and later
Vendor Advisory: https://www.gryphonconnect.com/support/security-advisory
Restart Required: Yes
Instructions:
1. Log into Gryphon router admin interface. 2. Navigate to Settings > Firmware Update. 3. Check for and install GryphonOS 4.0.0 or later. 4. Reboot router after update completes.
🔧 Temporary Workarounds
Block port 9999 with firewall
linuxPrevent access to vulnerable service by blocking port 9999 at network perimeter.
iptables -A INPUT -p tcp --dport 9999 -j DROP
iptables -A INPUT -p udp --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 network to limit access only to trusted administrative systems
- Implement strict network monitoring for traffic to port 9999 and alert on suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check if controller_server is listening on port 9999: 'netstat -tulpn | grep :9999' or 'ss -tulpn | grep :9999'. If service is running and version is below GryphonOS 4.0.0, device is vulnerable.Check Version:
Check router admin interface at Settings > About or run 'cat /etc/gryphon-version' on device shell if accessible.Verify Fix Applied:
Verify GryphonOS version is 4.0.0 or later in admin interface and confirm controller_server no longer accepts malicious operation 41 packets.📡 Detection & Monitoring
Log Indicators:
- Unusual process execution from controller_server
- Failed authentication attempts on port 9999 (though exploit is unauthenticated)
- Suspicious command strings in system logs
Network Indicators:
- TCP/UDP traffic to port 9999 from unexpected sources
- Malformed packets to port 9999 containing shell metacharacters
SIEM Query:
source_port:9999 AND (payload_contains:";" OR payload_contains:"|" OR payload_contains:"`" OR payload_contains:"$")