CVE-2025-5839
📋 TL;DR
A critical buffer overflow vulnerability in Tenda AC9 routers allows remote attackers to execute arbitrary code by sending specially crafted POST requests to the /goform/AdvSetLanip endpoint. This affects Tenda AC9 routers running firmware version 15.03.02.13. Attackers can exploit this without authentication to potentially take full control of affected devices.
💻 Affected Systems
- Tenda AC9
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, persistent backdoor installation, network traffic interception, and lateral movement to other devices on the network.
Likely Case
Remote code execution allowing attackers to modify router settings, intercept network traffic, or use the device as part of a botnet.
If Mitigated
Limited impact if devices are behind firewalls with strict inbound filtering or in isolated network segments.
🎯 Exploit Status
Exploit details have been publicly disclosed, making weaponization likely. The vulnerability requires no authentication and has a straightforward exploitation path.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.tenda.com.cn/
Restart Required: Yes
Instructions:
1. Check Tenda's official website for firmware updates. 2. If available, download the latest firmware for AC9. 3. Log into router admin interface. 4. Navigate to firmware upgrade section. 5. Upload and apply the new firmware. 6. Reboot the router.
🔧 Temporary Workarounds
Network Segmentation
allIsolate Tenda AC9 routers from untrusted networks and restrict access to management interfaces.
Access Control Lists
linuxImplement firewall rules to block external access to router management interfaces.
iptables -A INPUT -p tcp --dport 80 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Replace affected Tenda AC9 routers with devices from vendors providing security updates.
- Place routers behind dedicated firewalls with strict inbound filtering rules.
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via admin interface. If version is exactly 15.03.02.13, the device is vulnerable.Check Version:
Login to router admin interface and check System Status or Firmware Version page.Verify Fix Applied:
Verify firmware version has changed from 15.03.02.13 to a newer version after patching.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /goform/AdvSetLanip
- Multiple failed buffer overflow attempts in system logs
- Unexpected router reboots or configuration changes
Network Indicators:
- Unusual outbound connections from router to unknown IPs
- Traffic patterns suggesting device compromise
SIEM Query:
source="router_logs" AND (url="/goform/AdvSetLanip" OR message="buffer overflow" OR message="segmentation fault")