Zyxel NAS Devices: Critical Vulnerabilities and Patch Updates

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In the dynamic realm of cybersecurity, where threats are ever-evolving, the importance of vigilance cannot be overstated. Recently, Zyxel, a prominent manufacturer of network-attached storage (NAS) devices, has unveiled a disconcerting revelation— a series of critical vulnerabilities that pose a severe risk to the security of your NAS device.

These vulnerabilities, if left unaddressed, have the potential to open a gateway for unauthorized access and control, putting your entire network infrastructure at the mercy of malicious actors. The implications are dire, ranging from the compromise of sensitive data to the infiltration of your network, painting a bleak picture of potential consequences.

As we mark the first anniversary of our awareness, it is imperative to delve into the specifics of these vulnerabilities and, more importantly, take immediate action to fortify our NAS devices against these looming threats. In this article, we explore the intricacies of the disclosed vulnerabilities and provide essential guidance on securing your NAS device and the invaluable data it safeguards.

The Vulnerabilities

Here are the critical vulnerabilities that have been identified in Zyxel NAS devices:

  1. CVE-2023-35137 (CVSS score: 7.5): This vulnerability in the authentication module of Zyxel NAS devices could allow an unauthenticated attacker to gain system information through a crafted URL, exploiting an improper authentication flaw.
  2. CVE-2023-35138 (CVSS score: 9.8): Here, a command injection flaw in the “show_zysync_server_contents” function permits an unauthenticated attacker to execute OS commands via a crafted HTTP POST request. This vulnerability is particularly alarming due to its high CVSS score, indicating a critical level of threat.
  3. CVE-2023-37927 (CVSS score: 8.8): This flaw arises from the improper neutralization of special elements in the CGI program of the NAS devices, enabling an authenticated attacker to execute OS commands through a tailored URL.
  4. CVE-2023-37928 (CVSS score: 8.8): A post-authentication command injection vulnerability in the WSGI server could let an authenticated attacker run OS commands via a specially crafted URL.
  5. CVE-2023-4473 (CVSS score: 9.8): Another command injection vulnerability, this time in the web server, allows an unauthenticated attacker to execute OS commands with a specially crafted URL. Its high CVSS score underlines the critical risk it poses.
  6. CVE-2023-4474 (CVSS score: 9.8): Similar to CVE-2023-4473, this vulnerability stems from improper neutralization in the WSGI server, enabling unauthenticated attackers to execute OS commands.

Patch Updates

Zyxel has responded promptly to these vulnerabilities and has released patches for the affected models, specifically NAS326 and NAS542. Owners of these models with firmware versions V5.21(AAZF.14)C0 and V5.21(ABAG.11)C0, respectively, are advised to upgrade to the patched versions V5.21(AAZF.15)C0 and V5.21(ABAG.12)C0 to mitigate these vulnerabilities.

It is crucial to prioritize the installation of these patches to ensure the security of your NAS device and the data it stores. Regularly updating your device’s firmware is a best practice to stay protected against emerging threats.

Protecting Your NAS Device

In addition to patching your device, here are some general security measures you can take to protect your NAS device:

  1. Change default passwords: Replace the default login credentials with strong, unique passwords to prevent unauthorized access.
  2. Enable two-factor authentication (2FA): Implementing 2FA adds an extra layer of security by requiring a second form of verification during the login process.
  3. Regularly update firmware: Stay up to date with the latest firmware releases from Zyxel and install them promptly to benefit from security enhancements and bug fixes.
  4. Disable unnecessary services: Disable any unnecessary services or features on your NAS device to minimize potential attack surfaces.
  5. Regularly backup data: Implement a robust backup strategy to ensure that your data is protected in case of a security incident or hardware failure.
  6. Monitor network activity: Keep an eye on your network traffic and look out for any suspicious activity or unauthorized access attempts.

By following these best practices, you can significantly enhance the security of your NAS device and safeguard your valuable data.


The disclosure of critical vulnerabilities in Zyxel NAS devices highlights the importance of staying vigilant in the face of evolving cyber threats. It is crucial to promptly install the provided patches and adopt recommended security measures to protect your NAS device and the data it holds. Regularly updating firmware, changing default passwords, and enabling 2FA are essential steps in maintaining a secure NAS environment. By prioritizing cybersecurity, you can mitigate the risks posed by these vulnerabilities and ensure the integrity of your network and data.

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