CVE-2026-71927 in VigorSwitch G2540xs
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a command injection vulnerability in the rebDevice function. The vulnerability is caused by insufficient filtering of the username and password fields before command execution. A remote attacker can trigger this vulnerability via crafted input to execute arbitrary commands with root privileges. Exploitation requires valid administrative credentials for the device's web management interface.
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Analysis
by VulDB Data Team • 08/24/2026
The DrayTek VigorSwitch series, a line of managed network switches widely deployed in enterprise and small-to-medium business environments, contains a critical command injection vulnerability within its embedded web management interface. This flaw specifically resides in the rebDevice function, which is responsible for handling device reconfiguration or reboot operations. The root cause of this security issue lies in insufficient input validation and sanitization mechanisms applied to the username and password fields prior to their use in system-level commands. When a user submits credentials through the web interface, these inputs are passed directly into shell command execution contexts without adequate filtering of special characters or metacharacters that could alter the intended command structure. This lack of proper boundary checking allows an attacker to inject arbitrary operating system commands by manipulating the input strings, effectively bypassing the application's logical controls and leveraging the underlying script interpreter to execute unintended operations on the host device.
From a technical perspective, this vulnerability represents a classic instance of OS Command Injection, categorized under CWE-78 in the Common Weakness Enumeration standard. The severity is significantly amplified by the fact that the vulnerable function operates with root privileges. In embedded Linux environments typical for network infrastructure devices, gaining command execution as the root user provides complete control over the operating system. This includes the ability to modify system configurations, install persistent backdoors, exfiltrate sensitive data such as configuration files containing plaintext credentials or encryption keys, and pivot into other segments of the internal network. The vulnerability is classified under MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter: Unix Shell, indicating that an attacker can leverage standard shell commands to interact with the compromised system.
The operational impact of this vulnerability extends beyond simple device compromise. Because DrayTek switches often serve as critical access points or distribution layers in network architectures, a successful exploitation could lead to widespread service disruption if an attacker chooses to crash the device or alter routing tables. Furthermore, since the switch manages VLANs and port security settings, compromising it allows an adversary to bypass network segmentation controls, facilitating lateral movement across trusted networks. The ability to execute commands as root means that attackers can disable logging mechanisms, tamper with firmware integrity checks, and establish persistent access that survives reboots if they modify startup scripts or cron jobs within the device's filesystem. This transforms a single compromised switch into a powerful foothold for advanced persistent threats targeting corporate infrastructure.
Exploitation of this vulnerability requires valid administrative credentials for the device's web management interface, which classifies it as an authenticated attack vector rather than an unauthenticated remote code execution flaw. While authentication requirements may seem to mitigate risk by limiting access to authorized personnel, they do not eliminate the threat entirely. Insider threats, stolen credentials from phishing attacks, or weak password policies can still provide attackers with the necessary entry point. Additionally, if administrative accounts are shared across multiple devices or have been exposed in previous data breaches, the attack surface remains viable for external adversaries who possess legitimate but compromised login details. The requirement for authentication does not negate the severity of the command injection itself; it merely defines the initial access condition required to trigger the flaw within the rebDevice function.
To mitigate this risk, organizations must prioritize immediate patching by upgrading DrayTek VigorSwitch firmware to versions that include fixes for this specific input validation issue. Until patches are applied or deployed, network administrators should restrict web management interface access using strict firewall rules, allowing connections only from trusted administrative IP addresses and disabling HTTP in favor of HTTPS with strong certificate verification where supported. It is also critical to enforce complex password policies and rotate credentials regularly to reduce the likelihood of credential compromise. Monitoring for unusual outbound traffic patterns or unexpected system logs related to shell execution can help detect potential exploitation attempts. Regular vulnerability assessments focused on network infrastructure components are essential to identify such misconfigurations before they can be leveraged by malicious actors seeking deeper access into enterprise networks.