CVE-2021-42890
📋 TL;DR
CVE-2021-42890 is a critical remote command injection vulnerability in TOTOLINK EX1200T routers that allows unauthenticated attackers to execute arbitrary commands with root privileges by exploiting the NTPSyncWithHost function. This affects all users running vulnerable firmware versions of the EX1200T router. Successful exploitation gives attackers complete control over the affected device.
💻 Affected Systems
- TOTOLINK EX1200T
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain full root access to the router, enabling them to intercept all network traffic, install persistent malware, pivot to internal networks, and use the device as part of a botnet.
Likely Case
Attackers compromise the router to redirect DNS, intercept credentials, or deploy cryptocurrency miners, potentially affecting all devices on the network.
If Mitigated
With proper network segmentation and firewall rules, impact is limited to the router itself, though attackers could still disrupt network connectivity.
🎯 Exploit Status
Public proof-of-concept code exists showing how to exploit the hostTime parameter injection. The vulnerability requires minimal technical skill to exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V4.1.2cu.5215_B20211224 or later
Vendor Advisory: https://www.totolink.net/
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to System Tools > Firmware Upgrade. 3. Download latest firmware from TOTOLINK website. 4. Upload and install firmware. 5. Reboot router after installation completes.
🔧 Temporary Workarounds
Disable remote management
allPrevent external access to router administration interface
Network segmentation
allIsolate router management interface to separate VLAN
🧯 If You Can't Patch
- Place router behind a firewall with strict inbound rules blocking all unnecessary ports
- Disable NTP synchronization feature if not required for operation
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router web interface under System Status > Firmware Version. If version is V4.1.2cu.5215 or earlier, device is vulnerable.Check Version:
curl -s http://router-ip/cgi-bin/cstecgi.cgi | grep -i versionVerify Fix Applied:
Verify firmware version shows V4.1.2cu.5215_B20211224 or later after patching. Test NTP functionality to ensure it still works without allowing command injection.📡 Detection & Monitoring
Log Indicators:
- Unusual NTP-related requests in router logs
- Suspicious commands in system logs
- Multiple failed login attempts followed by NTP requests
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains
- Unexpected SSH/Telnet connections to router
SIEM Query:
source="router.log" AND ("NTPSyncWithHost" OR "hostTime" OR suspicious command patterns)