CVE-2020-6760
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary operating system commands with root privileges on Schmid ZI 620 V400 VPN 090 routers. Attackers can exploit this by injecting shell metacharacters into SSH subcommand menu entries, such as the ping command. Organizations using these specific VPN routers are affected.
💻 Affected Systems
- Schmid ZI 620 V400 VPN 090 router
📦 What is this software?
Zi 620 V400 Firmware by Schmid Telecom
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the VPN router with root access, allowing attackers to intercept all VPN traffic, pivot to internal networks, install persistent backdoors, and disable security controls.
Likely Case
Attackers gain root shell access on the router, enabling them to monitor VPN traffic, steal credentials, and use the device as a foothold into the internal network.
If Mitigated
With proper network segmentation and access controls, impact is limited to the compromised router itself, though VPN traffic confidentiality could still be breached.
🎯 Exploit Status
Exploitation requires SSH access credentials, but once authenticated, command injection is straightforward via shell metacharacters in SSH subcommands.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V400 firmware with security update
Vendor Advisory: Not publicly documented
Restart Required: Yes
Instructions:
1. Contact Schmid Telecom for updated firmware. 2. Backup router configuration. 3. Apply firmware update via management interface. 4. Reboot router. 5. Verify update and restore configuration if needed.
🔧 Temporary Workarounds
Disable SSH access
allDisable SSH service on the router if not required for management.
Restrict SSH access
allLimit SSH access to specific management IP addresses using firewall rules.
🧯 If You Can't Patch
- Isolate the router in a dedicated network segment with strict firewall rules limiting inbound and outbound connections.
- Implement network monitoring and intrusion detection specifically for the router's management interface.
🔍 How to Verify
Check if Vulnerable:
Test SSH access to the router and attempt command injection via ping subcommand with shell metacharacters (e.g., ping 127.0.0.1; id).Check Version:
Check firmware version via router web interface or SSH command: show versionVerify Fix Applied:
After patching, retest command injection attempts; they should fail or return sanitized output.📡 Detection & Monitoring
Log Indicators:
- Unusual SSH login attempts
- Commands with shell metacharacters in SSH logs
- Unexpected process execution on router
Network Indicators:
- Anomalous outbound connections from router
- Unexpected traffic patterns through VPN
SIEM Query:
source="router_logs" AND ("ping;" OR "ping |" OR "ping $" OR "ping `")