CVE-2020-20746
📋 TL;DR
A stack-based buffer overflow vulnerability in the Tenda AC9 router's HTTP server allows remote attackers to execute arbitrary code or cause denial of service via a crafted POST request to /goform/SetStaticRouteCfg. This affects Tenda AC9 routers running firmware version V15.03.06.60_EN. Attackers can potentially gain full control of affected routers.
💻 Affected Systems
- Tenda AC9 router
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete router compromise, credential theft, network pivoting, and persistent backdoor installation.
Likely Case
Router crash causing denial of service, requiring physical reset and disrupting network connectivity.
If Mitigated
Limited to denial of service if exploit fails or is detected by security controls.
🎯 Exploit Status
Public proof-of-concept code exists in GitHub repositories. Exploitation requires sending a specially crafted HTTP POST request.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V15.03.06.61_EN or later (check Tenda website for latest)
Vendor Advisory: https://www.tendacn.com/en/
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to System Tools > Firmware Upgrade. 3. Download latest firmware from Tenda website. 4. Upload and install firmware. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Disable remote administration
allPrevent external access to router admin interface
Login to router > Advanced > System Tools > Remote Management > Disable
Block vulnerable endpoint
linuxUse firewall rules to block access to /goform/SetStaticRouteCfg
iptables -A INPUT -p tcp --dport 80 -m string --string "POST /goform/SetStaticRouteCfg" --algo bm -j DROP
🧯 If You Can't Patch
- Replace router with different model/brand
- Place router behind separate firewall with strict inbound rules
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under System Status or System Tools > Firmware UpgradeCheck Version:
curl -s http://router-ip/goform/GetSysInfo | grep versionVerify Fix Applied:
Confirm firmware version is V15.03.06.61_EN or later after upgrade📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /goform/SetStaticRouteCfg with abnormal payload length
- Router crash/reboot logs
Network Indicators:
- Unusual HTTP traffic to router on port 80 with POST to vulnerable endpoint
- Router becoming unresponsive
SIEM Query:
source="router_logs" AND (url="/goform/SetStaticRouteCfg" OR message="crash" OR message="reboot")