CVE-2025-65221
📋 TL;DR
Tenda AC21 router firmware version V16.03.08.16 contains a buffer overflow vulnerability in the setPptpUserList function. Attackers can exploit this by sending specially crafted requests to the /goform/setPptpUserList endpoint, potentially causing denial of service or remote code execution. This affects all users running the vulnerable firmware version.
💻 Affected Systems
- Tenda AC21
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete router compromise, credential theft, and network infiltration
Likely Case
Router crash/reboot causing denial of service and network disruption
If Mitigated
Limited impact if network segmentation isolates router management interface
🎯 Exploit Status
Exploit requires authentication to router's web interface; buffer overflow in list parameter is straightforward to trigger
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: Yes
Instructions:
1. Check Tenda website for firmware updates
2. Download latest firmware for AC21
3. Log into router admin panel
4. Navigate to System Tools > Firmware Upgrade
5. Upload and install new firmware
6. Reboot router
🔧 Temporary Workarounds
Disable remote management
allPrevent external access to router's web interface
Change default credentials
allUse strong, unique admin password to reduce attack surface
🧯 If You Can't Patch
- Segment router management interface to isolated VLAN
- Implement network firewall rules to restrict access to router's web interface
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin panel under System StatusCheck Version:
Login to router web interface and check System Status pageVerify Fix Applied:
Verify firmware version is newer than V16.03.08.16📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by POST requests to /goform/setPptpUserList with long list parameter
Network Indicators:
- Unusual HTTP POST requests to router management interface with oversized parameters
SIEM Query:
source="router_logs" AND (uri="/goform/setPptpUserList" AND content_length>1000)