CVE-2021-20138
📋 TL;DR
An unauthenticated command injection vulnerability in Gryphon Tower routers allows attackers on the same network to execute arbitrary commands as root via the web interface. This affects all users of vulnerable Gryphon Tower router models, enabling complete device compromise without authentication.
💻 Affected Systems
- Gryphon Tower router
📦 What is this software?
Gryphon Tower Firmware by Gryphonconnect
⚠️ Risk & Real-World Impact
Worst Case
Complete router takeover allowing traffic interception, credential theft, network pivoting, and persistent backdoor installation.
Likely Case
Router compromise leading to DNS hijacking, credential harvesting, and network reconnaissance.
If Mitigated
Limited impact if network segmentation isolates routers and restricts access to management interfaces.
🎯 Exploit Status
Public exploit code available; exploitation requires only HTTP requests to vulnerable endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: GryphonOS 4.2.1 and later
Vendor Advisory: https://www.gryphonconnect.com/support/security-advisory
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to System > Firmware Update. 3. Check for and install GryphonOS 4.2.1 or later. 4. Reboot router after update completes.
🔧 Temporary Workarounds
Disable web interface access
linuxBlock access to router web interface from untrusted network segments
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
Network segmentation
allIsolate router management interface to dedicated VLAN
🧯 If You Can't Patch
- Segment router management interface to dedicated VLAN with strict access controls
- Implement network monitoring for suspicious HTTP requests to /cgi-bin/luci/rc endpoint
🔍 How to Verify
Check if Vulnerable:
Check GryphonOS version in router admin interface under System > About; versions below 4.2.1 are vulnerable.Check Version:
curl -s http://router-ip/cgi-bin/luci/ | grep -i versionVerify Fix Applied:
Confirm GryphonOS version is 4.2.1 or higher in System > About page.📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /cgi-bin/luci/rc with shell metacharacters
- Unusual command execution in router logs
Network Indicators:
- HTTP traffic to router IP on port 80/443 containing shell commands in POST parameters
SIEM Query:
source="router_logs" AND uri_path="/cgi-bin/luci/rc" AND (http_method="POST" OR contains(request_body, "$") OR contains(request_body, "|") OR contains(request_body, ";"))