CVE-2023-31447
📋 TL;DR
This vulnerability allows attackers to send crafted payloads to the user_login.cgi endpoint on affected Draytek Vigor devices, enabling arbitrary code execution by modifying memory segments and inserting shellcode. It affects Draytek Vigor2620 devices before firmware version 3.9.8.4 and all versions of Vigor2925 devices. Organizations using these devices as routers or firewalls are at risk.
💻 Affected Systems
- Draytek Vigor2620
- Draytek Vigor2925
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attackers to gain persistent access, pivot to internal networks, intercept/modify traffic, and use the device as a launch point for further attacks.
Likely Case
Remote code execution leading to device takeover, credential theft, network traffic interception, and potential lateral movement into connected networks.
If Mitigated
Limited impact if devices are behind firewalls with strict ingress filtering and network segmentation, though the vulnerability remains exploitable from internal networks.
🎯 Exploit Status
Public proof-of-concept code exists in GitHub gists. The vulnerability requires no authentication and has a straightforward exploitation path for remote code execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Vigor2620: 3.9.8.4 or later; Vigor2925: Check Draytek for latest firmware
Vendor Advisory: https://draytek.com
Restart Required: Yes
Instructions:
1. Log into device web interface. 2. Navigate to System Maintenance > Firmware Upgrade. 3. Download latest firmware from Draytek support site. 4. Upload and apply firmware update. 5. Reboot device after update completes.
🔧 Temporary Workarounds
Network Access Control
allRestrict access to device management interface using firewall rules or ACLs
Disable Web Management
allDisable web-based management interface if alternative management methods are available
🧯 If You Can't Patch
- Isolate affected devices in dedicated network segments with strict firewall rules limiting inbound connections
- Implement network monitoring and intrusion detection specifically for traffic to/from the device management interface
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface: System Maintenance > Firmware InformationCheck Version:
No CLI command; check via web interface or SNMP if configuredVerify Fix Applied:
Verify firmware version is 3.9.8.4 or later for Vigor2620, or latest available for Vigor2925📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /cgi-bin/user_login.cgi
- Multiple failed login attempts followed by successful exploitation
- Unexpected process execution or configuration changes
Network Indicators:
- Unusual outbound connections from device
- Traffic patterns suggesting command-and-control communication
- Exploit payloads in HTTP requests to management interface
SIEM Query:
source_ip="device_management_ip" AND (uri_path="/cgi-bin/user_login.cgi" OR http_method="POST" AND user_agent CONTAINS "exploit")