CVE-2021-45742
📋 TL;DR
This CVE describes a command injection vulnerability in TOTOLINK A720R routers that allows attackers to execute arbitrary commands via the QUERY_STRING parameter. Attackers can gain full control of affected devices, potentially compromising network security. Users of TOTOLINK A720R routers with vulnerable firmware are affected.
💻 Affected Systems
- TOTOLINK A720R
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device takeover leading to network compromise, data exfiltration, lateral movement to other devices, and persistent backdoor installation.
Likely Case
Router compromise allowing traffic interception, DNS manipulation, credential theft, and use as attack platform.
If Mitigated
Limited impact with proper network segmentation, firewall rules, and monitoring detecting exploitation attempts.
🎯 Exploit Status
Public proof-of-concept available in GitHub repository; exploitation requires sending crafted HTTP requests to vulnerable endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: Yes
Instructions:
1. Check TOTOLINK website for firmware updates
2. If update available, download and verify checksum
3. Access router admin interface
4. Navigate to firmware update section
5. Upload new firmware file
6. Wait for reboot and verify version
🔧 Temporary Workarounds
Network Isolation
allPlace router behind firewall with restricted inbound access
Access Control
linuxRestrict admin interface access to trusted IP addresses only
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
- Replace affected router with different model/brand
- Implement strict network segmentation to limit router access
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface; if version matches v4.1.5cu.470_B20200911, device is vulnerable.Check Version:
curl -s http://router-ip/version or check web interfaceVerify Fix Applied:
Verify firmware version has changed from vulnerable version; test with known safe payloads if possible.📡 Detection & Monitoring
Log Indicators:
- Unusual command execution in router logs
- HTTP requests with shell metacharacters in QUERY_STRING
- Unexpected process creation
Network Indicators:
- HTTP requests to router with suspicious parameters
- Outbound connections from router to unexpected destinations
- DNS queries from router to malicious domains
SIEM Query:
source="router_logs" AND (QUERY_STRING CONTAINS "|" OR QUERY_STRING CONTAINS ";" OR QUERY_STRING CONTAINS "`")