Zyxel VMG4325-B10A Legacy DSL CPE CGI Program Remote Command Injection Vulnerability (CVE-2024-40890) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTZyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615 and prior
An authenticated attacker can execute arbitrary operating system (OS) commands with system privileges by sending a crafted HTTP POST request to the CGI program
Since this is an end-of-life (EOL) legacy device, immediate hardware replacement or strict access control restricting WAN-side management access is highly recommended
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
This product is legacy and unsupported (EOL); therefore, no official security patches or firmware updates will be released by the vendor. The primary recommendation is to decommission the device and replace it with a supported model. If immediate replacement is not feasible, apply the following workarounds.
2. Temporary Workaround & Hardening Configuration
Disable external WAN-side access to the web management interface. Use firewall rules to restrict access to trusted internal IP addresses only.
# Block all incoming HTTP/HTTPS traffic to the management interface from the WAN interface (e.g., eth0)
iptables -A INPUT -i eth0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -j DROP
# Allow access only from a trusted internal administration subnet
iptables -A INPUT -s 192.168.1.0/24 -p tcp --dport 443 -j ACCEPT3. Log Audit & IoC Verification Commands
Verify the current firmware version and inspect web server logs for potential command injection attempts using the following commands:
# 1. Check the running firmware version on the device
cat /etc/release 2>/dev/null || uname -a
# 2. Audit web server logs for suspicious shell metacharacters in CGI requests
grep -E 'cgi-bin.*(\;|\||\&|\`|\$)' /var/log/httpd/*.log 2>/dev/nullStop 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
This vulnerability (CVE-2024-40890) is a post-authentication command injection vulnerability located in the CGI program of the legacy Zyxel VMG4325-B10A DSL CPE device. The root cause is the lack of proper input validation and sanitization of user-supplied parameters before passing them to a system shell interpreter (CWE-78).
2. Exploitation Mechanics & Attack Scenario
To exploit this vulnerability, an attacker must first authenticate to the web management interface using valid credentials. Once authenticated, the attacker sends a specially crafted HTTP POST request targeting the vulnerable CGI script. By embedding shell metacharacters (such as ';', '&', or '|') along with malicious OS commands into the request parameters, the CGI program executes the injected commands on the underlying operating system with the privileges of the web server.
3. Infrastructure & Business Impact
With a CVSS score of 8.8 and its inclusion in the CISA KEV catalog, this vulnerability poses a severe threat as it is actively exploited in the wild. Successful exploitation allows complete compromise of the CPE device, enabling attackers to establish persistent access, pivot into the internal local network, sniff network traffic, or enlist the device into a malicious botnet.
Official Vendor Advisories & References
**UNSUPPORTED WHEN ASSIGNED** A post-authentication command injection vulnerability in the CGI program of the legacy DSL CPE Zyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615 could allow an authenticated attacker to execute operating system (OS) commands on an affected device by sending a crafted HTTP POST request.
Frequently Asked SecOps Questions (CVE-2024-40890)
FAQQ1. How critical is CVE-2024-40890 and is it actively exploited in the wild?
CVE-2024-40890 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 20.7%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2024-40890?
Primary impacted vendors include zyxel across vmg4325-b10a. Scope summary: Zyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615 (Unsupported/EOL product)
Q3. What temporary mitigations or workarounds exist for CVE-2024-40890 before patching?
[Mitigation] Since this is an end-of-life (EOL) legacy device, immediate hardware replacement or strict access control restricting WAN-side management access is highly recommended 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-2024-40890
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