DrayTek VigorConnect WebServlet Local File Inclusion (LFI) Vulnerability (CVE-2021-20124) Technical Analysis and Hardening Guide
Executive & SecOps Summary
SECOPS ASSESSMENTDrayTek VigorConnect version 1.6.0-B3 and prior
Unauthenticated remote attackers can download arbitrary system files with root privileges via directory traversal
Immediately upgrade VigorConnect to the latest patched version (1.6.0-RC1 or higher) and restrict access to the management interface
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Download and install the latest secure version of VigorConnect from the official DrayTek portal. Use the following commands to update the service on a Linux host:
# Stop the VigorConnect service
sudo systemctl stop vigorconnect.service
# Download and install the updated package
wget https://www.draytek.com/ftp/VigorConnect/1.6.0/vigorconnect_1.6.0_amd64.deb
sudo dpkg -i vigorconnect_1.6.0_amd64.deb
# Restart and verify the service
sudo systemctl daemon-reload
sudo systemctl start vigorconnect.service
sudo systemctl status vigorconnect.service2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, implement a reverse proxy rule to block directory traversal patterns and restrict access to authorized IP addresses only.
# Nginx mitigation configuration
server {
listen 80;
server_name vigorconnect.local;
# Block directory traversal attempts
if ($request_uri ~* '(\.\./|\.\.\\)') {
return 403 'Access Denied: Malicious Request Blocked';
}
location / {
# Restrict access to trusted admin subnet
allow 192.168.10.0/24;
deny all;
proxy_pass http://127.0.0.1:8080;
}
}3. Log Audit & IoC Verification Commands
Run the following commands to inspect web server access logs for potential exploitation attempts targeting the WebServlet endpoint.
# Scan web logs for directory traversal patterns targeting WebServlet
echo '[+] Scanning logs for CVE-2021-20124 exploitation attempts...'
grep -Ei 'WebServlet.*(\.\.|%2e%2e)' /var/log/nginx/access.log /var/log/apache2/access.log 2>/dev/null
# Verify the running process privileges of VigorConnect
ps aux | grep -i vigorconnectStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
A local file inclusion (LFI) and directory traversal vulnerability (CWE-22) exists in the file download functionality of the WebServlet endpoint in DrayTek VigorConnect 1.6.0-B3. The root cause is the lack of proper input validation and sanitization on user-supplied file path parameters, allowing directory traversal sequences (../) to bypass intended directory boundaries.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated attacker can exploit this vulnerability by sending a crafted HTTP GET request containing directory traversal sequences to the vulnerable WebServlet endpoint. Because the VigorConnect service runs with root privileges, the application retrieves and returns any requested file from the underlying operating system, such as /etc/passwd or application configuration files containing sensitive credentials.
3. Infrastructure & Business Impact
This vulnerability is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and has an EPSS score of 0.9592, indicating active exploitation in the wild. Compromising a network management system like VigorConnect grants attackers deep visibility and potential control over the entire managed network infrastructure, posing severe risks of data exfiltration and lateral movement.
Official Vendor Advisories & References
A local file inclusion vulnerability exists in Draytek VigorConnect 1.6.0-B3 in the file download functionality of the WebServlet endpoint. An unauthenticated attacker could leverage this vulnerability to download arbitrary files from the underlying operating system with root privileges.
Frequently Asked SecOps Questions (CVE-2021-20124)
FAQQ1. How critical is CVE-2021-20124 and is it actively exploited in the wild?
CVE-2021-20124 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 95.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-20124?
Primary impacted vendors include draytek across vigorconnect. Scope summary: DrayTek VigorConnect version 1.6.0-B3 and earlier
Q3. What temporary mitigations or workarounds exist for CVE-2021-20124 before patching?
[Mitigation] Immediately upgrade VigorConnect to the latest patched version (1.6.0-RC1 or higher) and restrict access to the management interface Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2021-20124
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