CVE-2021-41653
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on TP-Link TL-WR840N EU v5 routers by sending a specially crafted payload to the PING function's IP address input field. Attackers can gain full control of affected routers without authentication. All users of the specified router model with vulnerable firmware are affected.
💻 Affected Systems
- TP-Link TL-WR840N EU v5 router
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router compromise allowing attackers to intercept all network traffic, install persistent malware, pivot to internal networks, and use the router as part of a botnet.
Likely Case
Router takeover leading to DNS hijacking, credential theft from network traffic, and use in DDoS attacks.
If Mitigated
Limited impact if router is behind firewall with restricted WAN access and network segmentation is implemented.
🎯 Exploit Status
Exploit requires sending crafted HTTP request to router's web interface. Public proof-of-concept code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware newer than TL-WR840N(EU)_V5_171211
Vendor Advisory: https://www.tp-link.com/us/press/security-advisory/
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to System Tools > Firmware Upgrade. 3. Download latest firmware from TP-Link support site. 4. Upload and install firmware. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to router web interface
Restrict WAN Access
allConfigure firewall to block external access to router admin interface
🧯 If You Can't Patch
- Replace router with non-vulnerable model
- Place router behind dedicated firewall with strict inbound rules
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under System Tools > Firmware Upgrade. If version is TL-WR840N(EU)_V5_171211 or older, device is vulnerable.Check Version:
Check router web interface or use nmap scan to identify firmware versionVerify Fix Applied:
Verify firmware version shows newer than TL-WR840N(EU)_V5_171211 after update.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP POST requests to /userRpm/pingIframeRpm.htm
- Multiple failed ping attempts with malformed IP addresses
- Unexpected router configuration changes
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains
- Traffic redirection patterns
SIEM Query:
source_ip=router_ip AND (url_path="/userRpm/pingIframeRpm.htm" OR user_agent CONTAINS "curl" OR user_agent CONTAINS "wget")