CVE-2025-63835
📋 TL;DR
A stack-based buffer overflow vulnerability in Tenda AC18 routers allows remote attackers to crash the device or potentially execute arbitrary code by sending oversized data to the guestSsid parameter. This affects Tenda AC18 routers running firmware version 15.03.05.05_multi. Attackers can exploit this without authentication over the network.
💻 Affected Systems
- Tenda AC18
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, persistent backdoor installation, and lateral movement into internal networks.
Likely Case
Denial of service causing device crash and network disruption, requiring physical reboot to restore functionality.
If Mitigated
Limited to denial of service if exploit mitigations like ASLR/NX are effective, but device still crashes.
🎯 Exploit Status
Public proof-of-concept code demonstrates reliable denial of service. Remote code execution would require additional exploit development but is feasible given the buffer overflow nature.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No vendor advisory found at time of analysis
Restart Required: Yes
Instructions:
1. Check Tenda website for firmware updates. 2. Download latest firmware for AC18 model. 3. Access router admin interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and install new firmware. 6. Reboot router after installation.
🔧 Temporary Workarounds
Disable Guest WiFi
allDisable the guest WiFi feature to remove access to the vulnerable /goform/WifiGuestSet interface.
Access router admin interface > Wireless Settings > Guest Network > Disable Guest WiFi
Network Segmentation
allIsolate Tenda AC18 routers in separate VLAN with strict firewall rules blocking access to management interfaces.
Configure firewall to block external access to port 80/443 on router IP
Create separate VLAN for IoT devices
🧯 If You Can't Patch
- Disable guest WiFi feature immediately through admin interface
- Block external WAN access to router management interface using firewall rules
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under System Status or System Tools > Firmware Upgrade page.Check Version:
curl -s http://router-ip/goform/getStatus | grep version or check web interfaceVerify Fix Applied:
Verify firmware version has changed from v15.03.05.05_multi to a newer version, and test that guest WiFi functionality still works if needed.📡 Detection & Monitoring
Log Indicators:
- Repeated POST requests to /goform/WifiGuestSet with large payloads
- Router crash/reboot events in system logs
- Unusual network traffic to router management interface
Network Indicators:
- HTTP POST requests to /goform/WifiGuestSet with oversized guestSsid parameter (> normal SSID length)
- Sudden loss of connectivity to router
SIEM Query:
http.method:POST AND http.uri:"/goform/WifiGuestSet" AND http.request_body:"guestSsid=" AND bytes > 500