CVE-2020-25366
📋 TL;DR
This vulnerability in D-Link DIR-823G routers allows attackers to cause denial of service (DoS) by exploiting an unspecified issue in the firmware upload CGI component. Attackers can crash or disrupt the router's functionality, affecting all users of vulnerable devices. The high CVSS score indicates significant impact potential.
💻 Affected Systems
- D-Link DIR-823G
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router failure requiring physical reset or replacement, disrupting all network connectivity for connected devices.
Likely Case
Router becomes unresponsive or reboots unexpectedly, causing temporary network outages until manual intervention.
If Mitigated
Minimal impact if device is behind firewall with restricted access to management interface.
🎯 Exploit Status
Public GitHub repository contains exploit details and proof-of-concept. Attack vectors unspecified but likely simple HTTP requests.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check D-Link security bulletin for latest firmware
Vendor Advisory: https://www.dlink.com/en/security-bulletin/
Restart Required: Yes
Instructions:
1. Visit D-Link support site 2. Download latest firmware for DIR-823G REVA1 3. Log into router admin interface 4. Navigate to firmware update section 5. Upload and apply new firmware 6. Wait for automatic reboot
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to router management interface
Log into router admin → System → Remote Management → Disable
Block CGI Access via Firewall
linuxRestrict access to /cgi-bin/upload_firmware.cgi endpoint
iptables -A INPUT -p tcp --dport 80 -m string --string "/cgi-bin/upload_firmware.cgi" --algo bm -j DROP
🧯 If You Can't Patch
- Isolate router on separate VLAN with strict access controls
- Implement network monitoring for unusual requests to /cgi-bin/upload_firmware.cgi
🔍 How to Verify
Check if Vulnerable:
Check router web interface → Status → Device Info for model DIR-823G REVA1 and firmware 1.02B05Check Version:
curl -s http://router-ip/ | grep -i firmwareVerify Fix Applied:
After firmware update, verify version changed from 1.02B05 to newer version📡 Detection & Monitoring
Log Indicators:
- Multiple failed or unusual requests to /cgi-bin/upload_firmware.cgi
- Router reboot events without user action
Network Indicators:
- HTTP POST requests to upload_firmware.cgi from unexpected sources
- Sudden loss of router responsiveness
SIEM Query:
source="router.log" AND (uri="/cgi-bin/upload_firmware.cgi" OR event="reboot")