CVE-2020-5757
📋 TL;DR
This vulnerability allows authenticated remote attackers to execute arbitrary operating system commands with root privileges on Grandstream UCM6200 series devices. Attackers can bypass existing command injection mitigations by sending specially crafted HTTP POST requests to the HTTPS API. Organizations using affected firmware versions are at risk of complete system compromise.
💻 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 takeover with root access, allowing installation of persistent backdoors, data exfiltration, lateral movement to other systems, and disruption of telephony services.
Likely Case
Unauthorized command execution leading to service disruption, credential theft, and potential ransomware deployment on the affected device.
If Mitigated
Limited impact if network segmentation restricts access to the management interface and strong authentication controls are in place.
🎯 Exploit Status
Exploitation requires valid credentials but is straightforward once authenticated. Public proof-of-concept code exists.
🛠️ 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 firmware version 1.0.20.24 or later from Grandstream support portal. 2. Log into UCM web interface. 3. Navigate to Maintenance > Upgrade. 4. Upload the firmware file. 5. Confirm upgrade and wait for automatic reboot.
🔧 Temporary Workarounds
Restrict API Access
allLimit network access to the UCM HTTPS API interface using firewall rules.
Strong Authentication Controls
allImplement complex passwords, multi-factor authentication, and account lockout policies for administrative accounts.
🧯 If You Can't Patch
- Isolate the UCM device on a separate VLAN with strict firewall rules limiting inbound connections to trusted management IPs only.
- Implement network monitoring and intrusion detection specifically for command injection patterns in HTTP POST requests to the UCM API endpoints.
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface: Login > Status > System Status > Firmware Version. If version is 1.0.20.23 or lower, device is vulnerable.Check Version:
curl -k https://<UCM_IP>/cgi-bin/api-sys_operation?passcode=<admin_pass> | grep FirmwareVersionVerify Fix Applied:
After patching, verify firmware version shows 1.0.20.24 or higher in the System Status page.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /cgi-bin/api-* endpoints
- Multiple failed authentication attempts followed by successful login and POST requests
- System logs showing unexpected command execution or process creation
Network Indicators:
- HTTP POST requests containing shell metacharacters (;, |, &, $, `) to UCM API endpoints
- Outbound connections from UCM to unexpected external IPs
SIEM Query:
source="UCM_logs" AND (uri_path="/cgi-bin/api-*" AND method="POST" AND (content="*;*" OR content="*|*" OR content="*`*" OR content="*$(*"))