CVE-2024-6342: Zyxel NAS326 Firmware RCE Vulnerability

CVE-2024-6342 Overview

A command injection vulnerability has been identified in the export-cgi program of Zyxel NAS326 and NAS542 firmware. This vulnerability allows an unauthenticated attacker to execute arbitrary operating system commands by sending a crafted HTTP POST request to the affected device. Notably, this vulnerability was assigned the status of UNSUPPORTED WHEN ASSIGNED, indicating that the affected products have reached end-of-life and may not receive official patches from the vendor.

Critical Impact

Unauthenticated remote attackers can execute arbitrary OS commands on vulnerable Zyxel NAS devices, potentially leading to complete system compromise, data theft, ransomware deployment, or use of the device as a pivot point for further network attacks.

Affected Products

• Zyxel NAS326 firmware versions through V5.21(AAZF.18)C0
• Zyxel NAS542 firmware versions through V5.21(ABAG.15)C0
• Zyxel NAS326 hardware devices
• Zyxel NAS542 hardware devices

Discovery Timeline

• September 10, 2024 - CVE-2024-6342 published to NVD
• January 22, 2025 - Last updated in NVD database

Technical Details for CVE-2024-6342

Vulnerability Analysis

This vulnerability is classified as OS Command Injection (CWE-78), which occurs when an application fails to properly sanitize user-supplied input before passing it to a system shell for execution. In the case of CVE-2024-6342, the vulnerable export-cgi component within the Zyxel NAS web interface does not adequately validate or sanitize input from HTTP POST requests.

The network-accessible nature of this vulnerability is particularly concerning because no authentication is required to exploit it. An attacker with network access to the NAS device's web management interface can craft a malicious HTTP POST request containing OS command sequences that will be executed with the privileges of the web server process, typically root on embedded NAS devices.

Root Cause

The root cause of this vulnerability lies in improper input validation within the export-cgi program. When processing HTTP POST requests, the application fails to sanitize user-controlled input before incorporating it into system commands. This allows an attacker to inject shell metacharacters and arbitrary commands that the underlying operating system will execute.

The vulnerability follows a classic command injection pattern where user input is concatenated with system commands without proper escaping or validation, enabling attackers to break out of the intended command context and execute arbitrary code.

Attack Vector

The attack vector for CVE-2024-6342 is network-based, requiring the attacker to have access to the NAS device's web management interface. The exploitation process involves:

1. The attacker identifies a vulnerable Zyxel NAS326 or NAS542 device exposed to the network
2. A specially crafted HTTP POST request is sent to the export-cgi endpoint
3. The malicious payload contains shell metacharacters and commands
4. The export-cgi program processes the request without proper sanitization
5. Injected OS commands are executed on the underlying system

Since no authentication is required, this vulnerability can be exploited by any attacker with network access to the device, making internet-exposed NAS devices particularly vulnerable.

The vulnerability allows command injection through the export-cgi endpoint via crafted HTTP POST parameters. Attackers can leverage shell metacharacters such as semicolons, pipes, or command substitution to inject malicious commands into the processing flow. For detailed technical information, refer to the Zyxel Security Advisory.

Detection Methods for CVE-2024-6342

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/export-cgi or similar CGI endpoints containing shell metacharacters
• Unexpected outbound network connections from NAS devices to external IP addresses
• Creation of unauthorized user accounts or modification of system files on NAS devices
• Suspicious processes spawned by the web server (e.g., reverse shells, wget/curl downloads)
• Evidence of command injection patterns in web server access logs (semicolons, pipes, backticks in parameters)

Detection Strategies

• Monitor web server logs for HTTP POST requests to CGI endpoints containing command injection patterns (;, |, $(), backticks)
• Implement network intrusion detection rules to identify command injection attempts targeting Zyxel NAS devices
• Deploy endpoint detection and response (EDR) solutions on network segments containing NAS devices to detect post-exploitation activity
• Use asset inventory tools to identify all Zyxel NAS326 and NAS542 devices in your environment

Monitoring Recommendations

• Enable detailed logging on Zyxel NAS devices and forward logs to a centralized SIEM platform
• Establish baseline network behavior for NAS devices and alert on anomalies such as outbound connections to unusual ports
• Monitor for process execution anomalies on NAS devices, particularly shell processes spawned by web server components
• Configure alerts for authentication failures or successful logins from unexpected source IP addresses

How to Mitigate CVE-2024-6342

Immediate Actions Required

• Immediately restrict network access to affected Zyxel NAS devices by placing them behind a firewall
• Disable remote web management access from untrusted networks, especially the internet
• Conduct an audit to identify all Zyxel NAS326 and NAS542 devices in your environment
• Review NAS device logs for any indicators of exploitation
• Consider migrating data to supported NAS devices, as affected products are marked as unsupported

Patch Information

Zyxel has released a security advisory addressing this vulnerability. However, it is critical to note that this vulnerability was assigned with the status UNSUPPORTED WHEN ASSIGNED, indicating that the affected NAS326 and NAS542 products may have reached end-of-life. Organizations should consult the Zyxel Security Advisory for the latest information on available patches and support status.

For devices that are no longer supported, organizations should strongly consider replacing them with currently supported models to ensure continued security updates.

Workarounds

• Isolate affected NAS devices on a separate network segment with strict access controls
• Implement network-level access control lists (ACLs) to restrict management interface access to trusted administrator IPs only
• Use a VPN to access NAS management interfaces rather than exposing them directly to the network
• Disable unnecessary services and ports on the NAS devices to reduce the attack surface
• If possible, disable the web management interface entirely and manage devices through alternative means

# Example firewall rules to restrict NAS management access (iptables)
# Replace NAS_IP with your device's IP and ADMIN_IP with trusted management IP
iptables -A INPUT -d NAS_IP -p tcp --dport 80 -s ADMIN_IP -j ACCEPT
iptables -A INPUT -d NAS_IP -p tcp --dport 443 -s ADMIN_IP -j ACCEPT
iptables -A INPUT -d NAS_IP -p tcp --dport 80 -j DROP
iptables -A INPUT -d NAS_IP -p tcp --dport 443 -j DROP