CVE-2021-28936
📋 TL;DR
This vulnerability allows unauthenticated attackers to change the administrator password on Acexy Wireless-N WiFi Repeater devices by sending a specially crafted HTTP GET request. Attackers only need to know the default admin username (admin) to exploit this flaw. All users of the affected device model with vulnerable firmware are at risk.
💻 Affected Systems
- Acexy Wireless-N WiFi Repeater REV 1.0
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the WiFi repeater allowing attackers to change network settings, intercept traffic, deploy malware to connected devices, or use the device as a pivot point into the internal network.
Likely Case
Unauthorized administrative access leading to network configuration changes, traffic monitoring, and potential credential theft from connected devices.
If Mitigated
Limited impact if device is behind firewall with restricted web interface access and strong network segmentation.
🎯 Exploit Status
Exploitation requires only a simple HTTP GET request with known default username. No authentication or special tools needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No vendor advisory found
Restart Required: No
Instructions:
No official patch available. Check manufacturer website for firmware updates. If unavailable, implement workarounds.
🔧 Temporary Workarounds
Disable Web Management Interface
allDisable the web management interface if not needed for regular operations
Check device documentation for disabling web interface
Network Access Control
linuxRestrict access to the repeater's management interface using firewall rules
iptables -A INPUT -p tcp --dport 80 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Replace vulnerable device with a secure alternative
- Isolate the repeater on a dedicated VLAN with strict firewall rules preventing management interface access
🔍 How to Verify
Check if Vulnerable:
Attempt to change admin password via HTTP GET request to device IP: http://device_ip/cgi-bin/webproc?getpage=html/index.html&var:username=admin&var:password=newpasswordCheck Version:
Check device web interface or console for firmware version informationVerify Fix Applied:
Attempt the same exploit after implementing controls - should fail or require authentication📡 Detection & Monitoring
Log Indicators:
- HTTP GET requests to /cgi-bin/webproc with password change parameters
- Failed login attempts followed by successful password change
Network Indicators:
- HTTP traffic to device management port (typically 80) containing password change parameters
- Unusual administrative access from unexpected IP addresses
SIEM Query:
source="web_logs" AND uri="/cgi-bin/webproc" AND (query="*password*" OR query="*var:*")