CVE-2021-27707
📋 TL;DR
This critical buffer overflow vulnerability in Tenda G1 and G3 routers allows remote attackers to execute arbitrary code by sending a specially crafted request to the port mapping functionality. Attackers can potentially take complete control of affected routers, which are typically deployed as perimeter devices. All users of affected Tenda router models with vulnerable firmware are at risk.
💻 Affected Systems
- Tenda G1
- Tenda G3
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router compromise leading to persistent backdoor installation, network traffic interception, credential theft, and lateral movement into internal networks.
Likely Case
Router takeover enabling man-in-the-middle attacks, DNS hijacking, credential harvesting, and botnet recruitment.
If Mitigated
Limited impact if routers are behind firewalls with strict ingress filtering and network segmentation.
🎯 Exploit Status
Public exploit details available in referenced research; exploitation requires sending crafted HTTP request to router web interface.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No official vendor advisory found
Restart Required: Yes
Instructions:
1. Check Tenda website for firmware updates
2. If update available, download and flash via router web interface
3. Factory reset after update to clear potential compromises
4. Verify firmware version post-update
🔧 Temporary Workarounds
Disable Remote Management
allDisable web interface access from WAN/Internet to prevent external exploitation
Router web interface: Advanced Settings > System Tools > Remote Management > Disable
Network Segmentation
allPlace routers in isolated network segment with strict firewall rules
🧯 If You Can't Patch
- Replace vulnerable routers with supported models from different vendors
- Implement strict network ACLs blocking all inbound traffic to router management interfaces
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via web interface: Status > Device InfoCheck Version:
curl -s http://router-ip/status.asp | grep firmwareVerify Fix Applied:
Verify firmware version is no longer v15.11.0.17(9502)_CN📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP POST requests to /goform/DelPortMapping
- Multiple failed login attempts followed by port mapping requests
- Router reboot logs without user action
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains
- Port scanning originating from router
SIEM Query:
source="router.log" AND ("DelPortMapping" OR "portMappingIndex") AND status=200