CVE-2026-3804
📋 TL;DR
A stack-based buffer overflow vulnerability in Tenda i3 routers allows remote attackers to execute arbitrary code by manipulating the 'index' parameter in the formWifiMacFilterSet function. This affects Tenda i3 router firmware version 1.0.0.6(2204). Attackers can exploit this remotely without authentication to potentially take full control of affected devices.
💻 Affected Systems
- Tenda i3
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, lateral movement to internal networks, persistent backdoor installation, and data exfiltration.
Likely Case
Device takeover enabling network traffic interception, DNS hijacking, credential theft, and use as botnet node for DDoS attacks.
If Mitigated
Limited impact if devices are behind firewalls with strict inbound filtering, though internal network exposure remains a concern.
🎯 Exploit Status
Public exploit code available on GitHub. Attack requires network access to router's web interface (typically port 80/443).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.tenda.com.cn/
Restart Required: Yes
Instructions:
1. Check Tenda website for firmware updates
2. Download latest firmware for i3 model
3. Access router admin interface
4. Navigate to firmware upgrade section
5. Upload and apply new firmware
6. Reboot router after update
🔧 Temporary Workarounds
Network Segmentation
allIsolate Tenda i3 routers from internet and critical internal networks
Access Control Lists
linuxRestrict access to router management interface to trusted IPs 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
- Replace affected Tenda i3 routers with supported/patched alternatives
- Disable remote management and WAN access to admin interface completely
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface under System Status or Firmware Upgrade sectionCheck Version:
curl -s http://router-ip/ | grep -i 'firmware\|version' or check web interfaceVerify Fix Applied:
Verify firmware version is no longer 1.0.0.6(2204) after update📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /goform/WifiMacFilterSet
- Multiple failed buffer overflow attempts
- Unexpected router reboots or configuration changes
Network Indicators:
- Unusual outbound connections from router IP
- Traffic to known exploit repositories
- Port scanning originating from router
SIEM Query:
source="router_logs" AND (uri="/goform/WifiMacFilterSet" OR message="buffer overflow" OR message="segmentation fault")