CVE-2021-27246
📋 TL;DR
This vulnerability allows attackers on the same network to execute arbitrary code as root on TP-Link Archer A7 AC1750 routers without authentication. The flaw exists in the tdpServer endpoint's handling of MAC addresses, enabling stack pointer manipulation. Only users with affected router versions are impacted.
💻 Affected Systems
- TP-Link Archer A7 AC1750
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router compromise with root-level code execution, allowing attackers to intercept traffic, modify configurations, install persistent malware, or pivot to other network devices.
Likely Case
Router takeover leading to DNS hijacking, credential theft from network traffic, or installation of backdoors for persistent access.
If Mitigated
Limited impact if router is isolated from critical systems, though still vulnerable to local network attacks.
🎯 Exploit Status
Exploit requires network access but no authentication. Technical details and proof-of-concept are publicly available through ZDI.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.0.16 or later
Vendor Advisory: https://www.tp-link.com/us/support/download/archer-a7/#Firmware
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to System Tools > Firmware Upgrade. 3. Download latest firmware from TP-Link website. 4. Upload and install firmware. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Disable tdpServer service
allDisable the vulnerable tdpServer endpoint if possible through router configuration
Network segmentation
allIsolate router management interface to trusted VLAN
🧯 If You Can't Patch
- Replace router with updated model or different vendor
- Implement strict network access controls to limit who can reach router management interface
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface under System Tools > Firmware UpgradeCheck Version:
Check router web interface or use nmap to identify firmware versionVerify Fix Applied:
Confirm firmware version is 1.0.16 or higher after update📡 Detection & Monitoring
Log Indicators:
- Unusual tdpServer activity
- Multiple failed connection attempts to router management ports
- Unexpected firmware modification logs
Network Indicators:
- Suspicious TCP traffic to router port 20002
- Unusual MAC address manipulation in network packets
- Anomalous outbound connections from router
SIEM Query:
source_ip=router_ip AND (port=20002 OR protocol=tdp) AND event_type=anomalous