CVE-2025-8939
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on Tenda AC20 routers by exploiting a buffer overflow in the WifiGuestSet function. Attackers can send specially crafted requests to the /goform/WifiGuestSet endpoint to gain control of affected devices. All users running Tenda AC20 firmware up to version 16.03.08.12 are affected.
💻 Affected Systems
- Tenda AC20
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise leading to persistent backdoor installation, network traffic interception, lateral movement to other devices, and botnet recruitment.
Likely Case
Remote code execution allowing attackers to modify router settings, intercept network traffic, or use the device as a pivot point for further attacks.
If Mitigated
Denial of service or temporary disruption if exploit fails or is detected by security controls.
🎯 Exploit Status
Proof-of-concept exploit code is publicly available on GitHub, making exploitation straightforward for attackers with basic skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: None known at this time
Restart Required: Yes
Instructions:
1. Check Tenda's official website for firmware updates. 2. Download the latest firmware for AC20. 3. Access router admin interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and install the new firmware. 6. Reboot the router.
🔧 Temporary Workarounds
Disable Wifi Guest Network
allDisable the guest WiFi functionality to remove the vulnerable endpoint
Block External Access to Admin Interface
allConfigure firewall rules to block external access to router management interface
🧯 If You Can't Patch
- Isolate affected routers in a separate network segment with strict firewall rules
- Implement network monitoring for unusual traffic patterns to/from router management interface
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via admin interface at System Status > Firmware VersionCheck Version:
curl -s http://router-ip/goform/GetSysInfo | grep firmwareVerify Fix Applied:
Verify firmware version is newer than 16.03.08.12 and test if /goform/WifiGuestSet endpoint responds to buffer overflow attempts📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /goform/WifiGuestSet with long shareSpeed parameters
- Router reboot events following suspicious requests
Network Indicators:
- HTTP requests with abnormally long parameters to router management interface
- Unusual outbound connections from router to unknown IPs
SIEM Query:
source="router-logs" AND uri="/goform/WifiGuestSet" AND parameter_length>1000🔗 References
- https://github.com/lin-3-start/lin-cve/blob/main/Tenda%20AC20/Tenda%20AC20.md
- https://github.com/lin-3-start/lin-cve/blob/main/Tenda%20AC20/Tenda%20AC20.md#3-poc
- https://vuldb.com/?ctiid.319902
- https://vuldb.com/?id.319902
- https://vuldb.com/?submit.631829
- https://www.tenda.com.cn/
- https://github.com/lin-3-start/lin-cve/blob/main/Tenda%20AC20/Tenda%20AC20.md
