CVE-2020-5759
📋 TL;DR
This vulnerability allows authenticated remote attackers to execute arbitrary operating system commands as root on Grandstream UCM6200 series devices via SSH command injection. Attackers can gain complete control of affected systems. Organizations using Grandstream UCM6200 series with firmware version 1.0.20.23 or below are affected.
💻 Affected Systems
- Grandstream UCM6200 series
📦 What is this software?
Ucm6202 Firmware by Grandstream
Ucm6204 Firmware by Grandstream
Ucm6208 Firmware by Grandstream
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to install persistent backdoors, exfiltrate sensitive data, pivot to internal networks, or render the device inoperable.
Likely Case
Attackers gaining root access to execute commands, potentially installing malware, modifying configurations, or using the device as a foothold for lateral movement.
If Mitigated
Limited impact if SSH access is restricted to trusted networks and authentication is properly secured with strong credentials.
🎯 Exploit Status
Exploitation requires authenticated SSH access. The vulnerability is in the 'unset' command handling.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.0.20.24 and above
Vendor Advisory: https://www.grandstream.com/support/security-advisories
Restart Required: Yes
Instructions:
1. Download latest firmware from Grandstream support portal. 2. Log into UCM6200 web interface. 3. Navigate to Maintenance > Upgrade. 4. Upload firmware file. 5. Click Upgrade and wait for reboot.
🔧 Temporary Workarounds
Disable SSH Access
linuxDisable SSH service if not required for operations
uci set dropbear.@dropbear[0].enable='0'
uci commit dropbear
/etc/init.d/dropbear restart
Restrict SSH Network Access
linuxLimit SSH access to specific trusted IP addresses using firewall rules
iptables -A INPUT -p tcp --dport 22 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate UCM6200 devices from critical networks
- Enforce strong password policies and consider multi-factor authentication for SSH access
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface: System Status > System Information > Firmware VersionCheck Version:
ssh admin@device_ip 'cat /etc/version'Verify Fix Applied:
Verify firmware version is 1.0.20.24 or higher after upgrade📡 Detection & Monitoring
Log Indicators:
- SSH logs showing 'unset' commands with unusual parameters
- System logs showing unexpected root command execution
Network Indicators:
- Unusual SSH connections to UCM6200 devices
- Outbound connections from UCM6200 to unexpected destinations
SIEM Query:
source="ssh_logs" AND "unset" AND ("|" OR ";" OR "$")