CVE-2026-3661
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary commands on Wavlink WL-NU516U1 routers by exploiting a command injection flaw in the firmware upgrade function. Attackers can manipulate the 'model' parameter to inject system commands, potentially gaining full control of affected devices. This affects all users of the vulnerable Wavlink router model.
💻 Affected Systems
- Wavlink WL-NU516U1
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attackers to install persistent backdoors, intercept network traffic, pivot to internal networks, or use the device for botnet activities.
Likely Case
Attackers gain shell access to execute commands, potentially stealing credentials, modifying device settings, or using the router as a foothold for further attacks.
If Mitigated
With proper network segmentation and access controls, impact is limited to the router itself without lateral movement to other systems.
🎯 Exploit Status
Exploit code is publicly available on GitHub, making this easily weaponizable by attackers with basic skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: Yes
Instructions:
1. Check Wavlink website for firmware updates
2. Download latest firmware for WL-NU516U1
3. Access router admin interface
4. Navigate to firmware upgrade section
5. Upload and apply new firmware
6. Reboot router after update
🔧 Temporary Workarounds
Disable Remote Administration
allPrevent external access to the vulnerable CGI endpoint by disabling remote administration features.
Access router admin panel -> Advanced Settings -> Remote Management -> Disable
Network Segmentation
allIsolate the router from critical internal networks to limit potential lateral movement.
Configure VLANs to separate router management traffic from production networks
🧯 If You Can't Patch
- Replace affected devices with patched or alternative models
- Implement strict firewall rules blocking all external access to port 80/443 on the router
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface. If version is 240425 or earlier, device is vulnerable.Check Version:
curl -s http://router-ip/cgi-bin/adm.cgi?action=version | grep firmwareVerify Fix Applied:
After firmware update, verify version has changed from 240425 and test if command injection payloads no longer execute.📡 Detection & Monitoring
Log Indicators:
- Unusual CGI requests to /cgi-bin/adm.cgi with shell metacharacters
- Multiple failed upgrade attempts
- Suspicious commands in system logs
Network Indicators:
- HTTP POST requests to /cgi-bin/adm.cgi containing shell commands
- Outbound connections from router to suspicious IPs
SIEM Query:
source="router-logs" AND uri="/cgi-bin/adm.cgi" AND (command="*;*" OR command="*|*" OR command="*`*" OR command="*$(*")