CVE-2021-45737
📋 TL;DR
This vulnerability is a stack overflow in the Form_Login function of TOTOLINK A720R routers, allowing attackers to cause Denial of Service (DoS) by sending specially crafted Host parameters. It affects users of TOTOLINK A720R routers running vulnerable firmware versions. The vulnerability can disrupt router functionality and network connectivity.
💻 Affected Systems
- TOTOLINK A720R
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router crash requiring physical reboot, persistent network downtime, and potential for remote code execution if the overflow can be controlled to execute arbitrary code.
Likely Case
Router becomes unresponsive, requiring reboot to restore functionality, causing temporary network disruption for connected devices.
If Mitigated
Limited impact with proper network segmentation and access controls preventing external exploitation attempts.
🎯 Exploit Status
Exploit details are publicly available in GitHub repositories. The vulnerability requires network access to the router's web interface.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: No
Instructions:
1. Check TOTOLINK website for firmware updates
2. If update available, download and install via web interface
3. Monitor vendor communications for security patches
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to router web interface
Access router settings > Administration > Remote Management > Disable
Network Segmentation
allIsolate router management interface from untrusted networks
Configure firewall rules to restrict access to router IP on port 80/443
🧯 If You Can't Patch
- Implement strict network access controls to limit who can reach the router management interface
- Monitor network traffic for abnormal login attempts or DoS patterns targeting the router
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in web interface under System > Firmware UpgradeCheck Version:
Not applicable - check via web interfaceVerify Fix Applied:
Verify firmware version is newer than v4.1.5cu.470_B20200911📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts
- Router reboot events
- Web interface access logs showing abnormal Host parameter values
Network Indicators:
- Unusual traffic to router management port (80/443)
- Router becoming unresponsive to ping/management
SIEM Query:
source="router_logs" AND (event="login_failure" OR event="reboot")