CVE-2025-65220
📋 TL;DR
A buffer overflow vulnerability in Tenda AC21 routers allows attackers to execute arbitrary code or crash the device by sending specially crafted requests to the /goform/SetVirtualServerCfg endpoint. This affects users running Tenda AC21 firmware version V16.03.08.16. The vulnerability requires network access to the router's web interface.
💻 Affected Systems
- Tenda AC21
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, persistent backdoor installation, and lateral movement to connected networks.
Likely Case
Device crash requiring physical reset, temporary denial of service, or limited information disclosure from memory corruption.
If Mitigated
No impact if the vulnerable endpoint is not accessible due to network segmentation or access controls.
🎯 Exploit Status
Proof of concept available in GitHub repository shows exploitation via HTTP POST request with crafted list parameter.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: No
Instructions:
1. Check Tenda website for firmware updates
2. If update available, download from official Tenda support site
3. Log into router web interface
4. Navigate to System Tools > Firmware Upgrade
5. Upload and apply the new firmware
6. Verify version after reboot
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to router web interface
Network Segmentation
allIsolate router management interface to trusted network
🧯 If You Can't Patch
- Implement strict network access controls to limit who can reach the router's web interface
- Monitor for unusual HTTP POST requests to /goform/SetVirtualServerCfg endpoint
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via web interface at System Status > Firmware VersionCheck Version:
curl -s http://router-ip/goform/getStatus | grep versionVerify Fix Applied:
Verify firmware version is no longer V16.03.08.16 after update📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /goform/SetVirtualServerCfg with unusually long list parameter
- Router crash/reboot events in system logs
Network Indicators:
- HTTP traffic to router IP on port 80/443 with POST to vulnerable endpoint
- Unusual outbound connections from router after exploitation
SIEM Query:
source="router_logs" AND (uri_path="/goform/SetVirtualServerCfg" AND content_length>1000)