CVE-2026-71931 in VigorSwitch
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a command injection vulnerability in the tftp_upgrade function. The vulnerability is caused by insufficient filtering before the filename field is concatenated into a command. 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 of network devices contains a critical security flaw within its firmware implementation, specifically located in the tftp_upgrade function responsible for handling Trivial File Transfer Protocol based system updates. This vulnerability stems from an improper input validation mechanism where user-supplied data is not adequately sanitized before being incorporated into operating system commands. The technical root cause lies in the direct concatenation of a filename field provided by the administrator without sufficient filtering or escaping, which allows special shell characters to be interpreted as executable code rather than literal file path components. This architectural weakness represents a classic instance of command injection, where the application fails to distinguish between data and instructions, thereby allowing an attacker to manipulate the intended execution flow of the system utility.
From a classification perspective, this vulnerability aligns with CWE-78, which defines Improper Neutralization of Special Elements used in an OS Command, commonly known as OS Command Injection. The flaw enables a remote authenticated user to bypass standard operational boundaries by injecting malicious payloads into the filename parameter during the upgrade process. Because the tftp_upgrade function typically operates with elevated privileges to modify system files and configurations, any command executed through this vector inherits those high-level permissions. Consequently, an attacker who successfully exploits this weakness gains full control over the underlying operating system of the network switch, effectively compromising the integrity, availability, and confidentiality of the device and potentially the broader network infrastructure it supports.
The operational impact of this vulnerability is severe due to its potential for complete device compromise. Although exploitation requires valid administrative credentials for the web management interface, which provides a layer of access control, the existence of such an entry point significantly lowers the barrier for attack if those credentials are obtained through phishing, brute force, or credential stuffing attacks. Once authenticated, the attacker can execute arbitrary commands with root privileges, allowing them to install persistent backdoors, exfiltrate sensitive network configuration data, pivot into other segments of the internal network, or disrupt service by modifying system parameters. This capability transforms a simple management interface vulnerability into a critical threat vector for lateral movement and deep infrastructure compromise within enterprise environments that rely on these switches for connectivity.
In terms of offensive security frameworks, this exploitation technique maps to MITRE ATT&CK techniques related to Command and Scripting Interpreter abuse, specifically the execution of system commands via injection points found in application interfaces. The attack pattern involves crafting a specific HTTP request or form submission where the filename field contains shell metacharacters such as semicolons, pipes, or backticks followed by malicious payloads. Defenders must recognize that even authenticated vulnerabilities can lead to full system takeover when privilege escalation is inherent to the function being exploited. Mitigation strategies should prioritize immediate application of vendor-provided firmware patches that address this input validation deficiency. In cases where patching is not immediately feasible, network segmentation and strict access control lists restricting management interface traffic to authorized IP addresses are essential compensating controls. Additionally, enforcing multi-factor authentication for administrative accounts reduces the likelihood of credential compromise, thereby mitigating the initial attack vector required to trigger this command injection flaw.