CVE-2020-3931
📋 TL;DR
This critical vulnerability allows unauthenticated remote attackers to execute arbitrary commands on Geovision Door Access Control devices via a buffer overflow. Attackers can gain complete control of affected devices without any authentication. Organizations using Geovision door access control systems are affected.
💻 Affected Systems
- Geovision Door Access Control devices
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to disable physical security controls, manipulate door access logs, install persistent backdoors, and pivot to internal networks.
Likely Case
Attackers gain remote code execution to disable door controls, steal access logs, or use devices as footholds for further network attacks.
If Mitigated
With proper network segmentation and access controls, impact limited to isolated physical security systems without lateral movement.
🎯 Exploit Status
Public exploit details available in security advisories. No authentication required for exploitation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware updates released in 2020
Vendor Advisory: https://www.twcert.org.tw/tw/cp-132-3754-b77d0-1.html
Restart Required: Yes
Instructions:
1. Contact Geovision for latest firmware. 2. Backup configuration. 3. Apply firmware update via web interface. 4. Reboot device. 5. Verify update successful.
🔧 Temporary Workarounds
Network Segmentation
allIsolate door access control devices from internet and internal networks
Access Control Lists
linuxRestrict network access to management interfaces
iptables -A INPUT -p tcp --dport 80 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Segment devices on isolated VLAN with strict firewall rules
- Disable web management interface if not required
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface and compare against patched versions from vendor advisoryCheck Version:
curl -s http://device_ip/cgi-bin/version.cgi or check web interfaceVerify Fix Applied:
Verify firmware version matches patched version and test management interface functionality📡 Detection & Monitoring
Log Indicators:
- Unusual command execution in system logs
- Multiple failed authentication attempts to management interface
- Unexpected process creation
Network Indicators:
- Unusual outbound connections from door controllers
- Exploit pattern traffic to port 80/tcp
- Shell command execution over HTTP
SIEM Query:
source="door_controller" AND (http.method="POST" AND http.uri="/cgi-bin/*" AND http.user_agent="exploit")🔗 References
- https://www.acronis.com/en-us/blog/posts/backdoor-wide-open-critical-vulnerabilities-uncovered-geovision
- https://www.twcert.org.tw/tw/cp-132-3754-b77d0-1.html
- https://www.acronis.com/en-us/blog/posts/backdoor-wide-open-critical-vulnerabilities-uncovered-geovision
- https://www.twcert.org.tw/tw/cp-132-3754-b77d0-1.html
