CVE-2021-46122
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on TP-Link TL-WR840N routers via a buffer overflow in the password reset feature. Attackers can exploit this without authentication to potentially take full control of affected devices. Only TP-Link TL-WR840N (EU) v6.20 routers with specific vulnerable firmware are affected.
💻 Affected Systems
- TP-Link TL-WR840N (EU) v6.20
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, persistent backdoor installation, network traffic interception, and lateral movement to other devices on the network.
Likely Case
Router compromise allowing attackers to change DNS settings, intercept traffic, or use the device as a pivot point for further attacks on the internal network.
If Mitigated
Limited impact if device is behind firewall with restricted WAN access, though internal attackers could still exploit if they gain network access.
🎯 Exploit Status
Public proof-of-concept exists demonstrating the buffer overflow. Exploitation requires sending specially crafted requests to the password reset endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check TP-Link support for latest firmware
Vendor Advisory: https://www.tp-link.com/support/download/tl-wr840n/v6/#Firmware
Restart Required: Yes
Instructions:
1. Visit TP-Link support page for TL-WR840N v6.20. 2. Download latest firmware. 3. Log into router admin interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and install new firmware. 6. Router will reboot automatically.
🔧 Temporary Workarounds
Disable remote management
allPrevents external attackers from accessing the vulnerable password reset feature
Login to router admin > Security > Remote Management > Disable
Change default admin password
allAdds authentication barrier though vulnerability is unauthenticated
Login to router admin > System Tools > Password > Set strong password
🧯 If You Can't Patch
- Replace vulnerable router with updated model or different vendor
- Place router behind firewall with strict inbound rules blocking all WAN access to management interface
🔍 How to Verify
Check if Vulnerable:
Check router web interface > Status page for firmware version matching vulnerable buildCheck Version:
curl -s http://router-ip/ | grep -i 'firmware version' or check router web interfaceVerify Fix Applied:
After firmware update, verify version no longer matches vulnerable build in Status page📡 Detection & Monitoring
Log Indicators:
- Multiple failed password reset attempts
- Unusual POST requests to password reset endpoint
- Buffer overflow error messages in system logs
Network Indicators:
- Unusual traffic to router management port (typically 80/443)
- POST requests with abnormally long password parameters
SIEM Query:
source="router_logs" AND (url_path="/password_reset" OR message="*buffer*overflow*")