CVE-2020-9054 in NAS
Summary
by MITRE
Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server does not run as the root user, ZyXEL devices include a setuid utility that can be leveraged to run any command with root privileges. As such, it should be assumed that exploitation of this vulnerability can lead to remote code execution with root privileges. By sending a specially-crafted HTTP POST or GET request to a vulnerable ZyXEL device, a remote, unauthenticated attacker may be able to execute arbitrary code on the device. This may happen by directly connecting to a device if it is directly exposed to an attacker. However, there are ways to trigger such crafted requests even if an attacker does not have direct connectivity to a vulnerable devices. For example, simply visiting a website can result in the compromise of any ZyXEL device that is reachable from the client system. Affected products include: NAS326 before firmware V5.21(AAZF.7)C0 NAS520 before firmware V5.21(AASZ.3)C0 NAS540 before firmware V5.21(AATB.4)C0 NAS542 before firmware V5.21(ABAG.4)C0 ZyXEL has made firmware updates available for NAS326, NAS520, NAS540, and NAS542 devices. Affected models that are end-of-support: NSA210, NSA220, NSA220+, NSA221, NSA310, NSA310S, NSA320, NSA320S, NSA325 and NSA325v2
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Analysis
by VulDB Data Team • 02/07/2025
This vulnerability represents a critical pre-authentication command injection flaw in ZyXEL network-attached storage devices that fundamentally undermines the security posture of affected systems. The vulnerability stems from inadequate input sanitization within the weblogin.cgi CGI executable, which processes the username parameter without proper validation or escaping mechanisms. This allows attackers to inject malicious commands that are subsequently executed by the web server, creating a pathway for remote code execution. The flaw operates at the application layer and affects devices running firmware versions prior to 5.21(AAZF.7)C0, 5.21(AASZ.3)C0, 5.21(AATB.4)C0, and 5.21(ABAG.4)C0 respectively, impacting a wide range of NAS models including NAS326, NAS520, NAS540, and NAS542. The vulnerability classification aligns with CWE-77 and CWE-94, which specifically address command injection and code injection weaknesses in web applications, making it a prime target for automated exploitation campaigns.
The operational impact of this vulnerability is severe and potentially catastrophic for affected organizations. Attackers can execute arbitrary code with root privileges through a simple HTTP POST or GET request, bypassing all authentication mechanisms. The web server component, while not running as root, leverages a setuid utility that can elevate privileges to root level, effectively providing attackers with complete system control. This includes the ability to access, modify, or delete all stored data, install backdoors, and establish persistent access to the network. The attack surface extends beyond direct network exposure, as attackers can trigger exploitation through web browsing activities, making it particularly dangerous for users who may inadvertently visit malicious websites. The vulnerability creates a persistent threat vector that can be exploited from anywhere on the internet, with no requirement for valid credentials or network proximity.
The exploitation mechanism demonstrates sophisticated attack patterns that align with ATT&CK framework techniques, particularly T1203 (Exploitation for Client Execution) and T1059 (Command and Scripting Interpreter). Attackers can craft malicious requests that leverage the vulnerable parameter to inject shell commands, potentially executing system-level operations such as creating new user accounts, modifying system files, or establishing reverse shells. The attack can be automated through web-based delivery methods, enabling large-scale exploitation campaigns that can compromise numerous devices simultaneously. Organizations with exposed ZyXEL NAS devices face immediate risk of data breaches, system compromise, and potential lateral movement within their networks, as these devices often serve as storage repositories for sensitive corporate data. The vulnerability's severity is compounded by the fact that many organizations may not be aware of their exposure, particularly in environments where legacy devices continue to operate without proper patch management protocols.
Mitigation strategies must address both immediate remediation and long-term security improvements. The primary solution involves applying the firmware updates provided by ZyXEL for all affected models, which properly sanitize the username parameter and prevent command injection attacks. Organizations should conduct comprehensive inventory audits to identify all potentially affected devices, including those that may be end-of-support and no longer receiving updates. Network segmentation should be implemented to isolate NAS devices from critical systems, and access controls should be enforced to limit exposure to only necessary personnel. Additional protective measures include implementing web application firewalls to detect and block suspicious requests, monitoring network traffic for exploitation attempts, and establishing robust patch management processes. Security teams should also consider disabling unnecessary services, implementing strong authentication for administrative access, and regularly auditing device configurations to prevent similar vulnerabilities from emerging in the future. The incident underscores the importance of maintaining up-to-date firmware and conducting regular security assessments of network infrastructure components.