CVE-2020-36178
📋 TL;DR
This CVE allows remote attackers to execute arbitrary operating system commands on TP-Link TL-WR840N routers by injecting malicious commands into an IP address field in the web interface. The vulnerability affects users of TP-Link TL-WR840N v6 routers with specific firmware versions. Attackers can gain full control of the device through command injection.
💻 Affected Systems
- TP-Link TL-WR840N
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router allowing attackers to intercept all network traffic, install persistent malware, pivot to internal networks, and use the device as part of a botnet.
Likely Case
Router takeover enabling traffic interception, DNS hijacking, credential theft, and lateral movement to connected devices.
If Mitigated
Limited impact if web interface access is restricted and proper network segmentation is implemented.
🎯 Exploit Status
Exploitation requires access to the web interface (typically requires authentication). The vulnerability is in a POST parameter that accepts raw input for iptables commands.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check TP-Link support for latest firmware
Vendor Advisory: https://www.tp-link.com/fr/support/download/tl-wr840n/v6/#Firmware
Restart Required: Yes
Instructions:
1. Log into TP-Link support portal. 2. Download latest firmware for TL-WR840N v6. 3. Access router web interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and install new firmware. 6. Router will reboot automatically.
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to the web interface by disabling remote management features.
Restrict Web Interface Access
linuxUse firewall rules to limit access to the router's web interface to trusted IP addresses only.
iptables -A INPUT -p tcp --dport 80 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Disable the web interface completely and use alternative management methods
- Replace affected devices with patched or different models
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in web interface under System Tools > Firmware Upgrade. If version is 0.9.1 4.16 or similar vulnerable version, device is affected.Check Version:
Check web interface at System Tools > Firmware Upgrade or via SSH if available: cat /proc/versionVerify Fix Applied:
After firmware update, verify version has changed from vulnerable version. Test that input validation now properly sanitizes IP address fields.📡 Detection & Monitoring
Log Indicators:
- Unusual iptables commands in system logs
- Multiple failed login attempts followed by successful login
- Unexpected system command execution
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains
- Unexpected port scans originating from router
SIEM Query:
source="router_logs" AND ("iptables" OR "system" OR "exec") AND command="*;*" OR command="*|*" OR command="*`*"🔗 References
- https://github.com/therealunicornsecurity/therealunicornsecurity.github.io/blob/master/_posts/2020-10-11-TPLink.md
- https://therealunicornsecurity.github.io/TPLink/
- https://www.tp-link.com/fr/support/download/tl-wr840n/v6/#Firmware
- https://github.com/therealunicornsecurity/therealunicornsecurity.github.io/blob/master/_posts/2020-10-11-TPLink.md
- https://therealunicornsecurity.github.io/TPLink/
- https://www.tp-link.com/fr/support/download/tl-wr840n/v6/#Firmware
