CVE-2026-71928 in VigorSwitch
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a command injection vulnerability in the fdftDevice 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 resides specifically in the fdftDevice function, which is responsible for handling device configuration tasks related to Fast Domain Name System (FDFT) or similar diagnostic features depending on firmware version specifics. The core technical deficiency lies in the insufficient sanitization and validation of user-supplied input fields, particularly those designated for username and password authentication during administrative operations. When a request containing these parameters reaches the backend processing logic, the application fails to properly escape special characters such as semicolons, ampersands, or pipe symbols that are interpreted by the underlying operating system shell. Consequently, any maliciously crafted payload embedded within these fields is executed directly by the root-level process managing the switch's firmware, bypassing standard access controls and input validation routines designed to prevent arbitrary code execution.
From a technical perspective, this vulnerability represents a classic instance of OS Command Injection, categorized under CWE-78 in the Common Weakness Enumeration database. The severity is exacerbated because the affected function operates with elevated privileges, typically root or equivalent administrative rights within the embedded Linux environment powering the switch. Although exploitation requires an attacker to possess valid administrative credentials for the device's web interface, this does not mitigate the risk significantly given that many organizations reuse default passwords, employ weak credential policies, or suffer from compromised admin accounts due to other vectors such as phishing or brute-force attacks on exposed management ports. Once authenticated, a remote adversary can inject shell commands into the username or password fields of HTTP requests directed at the vulnerable endpoint. The web server then passes these unsanitized inputs directly to system-level command interpreters like sh or bash without adequate filtering, allowing the execution of arbitrary operating system commands with full root privileges.
The operational impact of this vulnerability is severe and multifaceted. An attacker who successfully exploits this flaw gains complete control over the affected network switch. This level of access allows for comprehensive reconnaissance of the internal network topology, interception of unencrypted traffic traversing the managed ports, and modification of switching rules to facilitate man-in-the-middle attacks or denial-of-service conditions against critical infrastructure services. Furthermore, because switches often serve as gateways between different network segments, compromising one device can provide a foothold for lateral movement into more sensitive parts of the corporate network, including servers hosting proprietary data or industrial control systems. The ability to execute commands with root privileges also enables persistence mechanisms such as installing backdoors, modifying system binaries, or altering firewall rules to maintain long-term access even if initial credentials are changed.
Mitigation strategies must prioritize immediate patching and rigorous credential management. DrayTek has released firmware updates that address this issue by implementing proper input validation and escaping mechanisms within the fdftDevice function to prevent shell metacharacters from being interpreted as commands. Administrators should upgrade their VigorSwitch devices to the latest stable firmware version provided by the vendor as soon as possible. In cases where immediate patching is not feasible due to operational constraints, temporary mitigations include restricting access to the web management interface through firewall rules to allow only trusted IP addresses or administrative subnets, thereby reducing the attack surface for remote exploitation. Additionally enforcing strong, unique passwords for all administrative accounts and disabling unused services can further reduce the likelihood of credential compromise leading to this specific exploit chain. Continuous monitoring of network traffic for anomalous patterns associated with command injection attempts may also aid in early detection of attempted exploits against unpatched systems.