CVE-2020-28250
📋 TL;DR
CVE-2020-28250 is a critical authentication bypass vulnerability in Cellinx NVT Web Server that allows remote attackers to execute arbitrary commands as root. The vulnerability exists because authentication is implemented on the client side, making it trivial to bypass. Any organization using the affected version of Cellinx NVT Web Server is at risk of complete system compromise.
💻 Affected Systems
- Cellinx NVT Web Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attacker gains full root access to the server, enabling data theft, ransomware deployment, lateral movement, and complete system destruction.
Likely Case
Attackers exploit this to install cryptocurrency miners, create persistent backdoors, or use the server as a pivot point for further attacks.
If Mitigated
With proper network segmentation and access controls, impact could be limited to the isolated server segment, though root compromise remains severe.
🎯 Exploit Status
Exploitation requires only HTTP requests to the vulnerable CGI endpoint. Public proof-of-concept code demonstrates trivial command injection.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
No official patch available. Consider upgrading to a newer version if available from Cellinx, or implement workarounds and compensating controls.
🔧 Temporary Workarounds
Block access to SetFileContent.cgi
linuxUse web server configuration or firewall rules to block all access to the vulnerable CGI endpoint.
# Example for iptables: iptables -A INPUT -p tcp --dport 80 -m string --string "SetFileContent.cgi" --algo bm -j DROP
# Example for Apache: <Location "/cgi-bin/SetFileContent.cgi"> Require all denied </Location>
Implement reverse proxy authentication
linuxPlace the server behind a reverse proxy that enforces proper authentication before requests reach the vulnerable endpoint.
# Configure nginx as reverse proxy with auth: location /cgi-bin/SetFileContent.cgi { auth_basic "Restricted"; auth_basic_user_file /etc/nginx/.htpasswd; proxy_pass http://cellinx_server; }
🧯 If You Can't Patch
- Immediately isolate the server in a dedicated VLAN with strict firewall rules allowing only necessary traffic
- Implement network-based intrusion detection to monitor for exploitation attempts and command execution patterns
🔍 How to Verify
Check if Vulnerable:
Test if SetFileContent.cgi endpoint is accessible without authentication and accepts arbitrary commands. Use: curl -X POST http://target/cgi-bin/SetFileContent.cgi --data 'command=id'Check Version:
Check web interface or configuration files for version information. Often displayed in web interface footer or about page.Verify Fix Applied:
Verify that SetFileContent.cgi endpoint is no longer accessible or requires proper authentication. Test with the same curl command should fail.📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /cgi-bin/SetFileContent.cgi
- Unusual command execution in system logs following web server requests
- Failed authentication attempts if logging is enabled
Network Indicators:
- HTTP traffic containing 'SetFileContent.cgi' in the URL
- POST requests to CGI endpoints with command parameters
- Unusual outbound connections from the web server
SIEM Query:
source="web_server_logs" AND url="*SetFileContent.cgi*" AND (method="POST" OR status="200")