CVE-2023-40942
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on Tenda AC9 routers via a stack overflow in the firewall configuration endpoint. Attackers can exploit this by sending specially crafted requests to the /goform/SetFirewallCfg URL. All users running the affected firmware version are vulnerable.
💻 Affected Systems
- Tenda AC9
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router leading to persistent backdoor installation, network traffic interception, credential theft, and lateral movement to connected devices.
Likely Case
Router takeover enabling DNS hijacking, credential harvesting from network traffic, and botnet recruitment.
If Mitigated
Limited impact if network segmentation isolates the router and external access is restricted.
🎯 Exploit Status
The GitHub reference contains technical details and likely exploit code. Stack overflow vulnerabilities in embedded devices are frequently weaponized.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Unknown
Restart Required: Yes
Instructions:
1. Check Tenda's official website for firmware updates. 2. Download the latest firmware for AC9. 3. Access router admin interface. 4. Navigate to firmware upgrade section. 5. Upload and apply the new firmware. 6. Reboot the router.
🔧 Temporary Workarounds
Disable remote management
allPrevent external access to the router's admin interface
Network segmentation
allIsolate the router from critical internal networks
🧯 If You Can't Patch
- Replace the router with a different model/vendor
- Implement strict firewall rules to block all access to the router's IP except from trusted management stations
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface. If version is V3.0BR_V15.03.06.42_multi_TD01, the device is vulnerable.Check Version:
Check via router web interface at 192.168.0.1 or 192.168.1.1 (default Tenda IPs)Verify Fix Applied:
After updating firmware, verify the version has changed from the vulnerable version.📡 Detection & Monitoring
Log Indicators:
- Multiple POST requests to /goform/SetFirewallCfg with unusual payloads
- Router crash/reboot logs
Network Indicators:
- Unusual traffic patterns from router to external IPs
- DNS queries to suspicious domains from router
SIEM Query:
source_ip=router_ip AND (url_path="/goform/SetFirewallCfg" OR http_method="POST" AND user_agent contains unusual patterns)