CVE-2026-71935 in VigorSwitch
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a buffer overflow vulnerability in the webBackupAction function. The vulnerability is caused by repeated string concatenation of the pathN, valueN, key, and option fields into fixed-size stack buffers without total length checks. A remote attacker can trigger this vulnerability via crafted input, causing a denial of service or potentially executing arbitrary commands. 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 identified vulnerability resides within the DrayTek VigorSwitch series of network hardware and specifically affects the webBackupAction function in the device’s embedded web server implementation. This flaw is classified as a classic buffer overflow, technically categorized under CWE-120: Buffer Copy without Checking Size of Input. The root cause stems from improper memory management practices where multiple user-supplied fields, including pathN, valueN, key, and option parameters, are concatenated into fixed-size stack buffers. Crucially, the implementation fails to perform bounds checking on the cumulative length of these inputs before copying them into the pre-allocated memory space. This lack of validation allows an attacker who provides sufficiently long or crafted input strings to exceed the buffer's capacity, thereby overwriting adjacent memory locations on the call stack.
From a technical perspective, this type of vulnerability is particularly dangerous because it can lead to control flow hijacking if the overflow reaches critical return addresses or function pointers stored on the stack. While the immediate observable effect may be a crash leading to a denial of service condition where the web management interface becomes unresponsive, more sophisticated exploitation could allow for arbitrary code execution with the privileges of the compromised process. In many embedded network devices, this process runs with elevated system rights, meaning successful exploitation could grant an attacker full control over the device’s operating environment. The vulnerability is exploitable remotely via HTTP requests directed at the web management interface, but it requires valid administrative credentials to access the specific endpoints that trigger the backup action logic. This requirement places the threat level in a context where insider threats or compromised admin accounts are primary vectors for exploitation.
The operational impact of this vulnerability extends beyond simple service disruption. If an attacker achieves code execution, they can potentially pivot from the managed switch to other devices on the local network segment by using the VigorSwitch as a foothold. This aligns with MITRE ATT&CK techniques related to Initial Access and Lateral Movement, specifically leveraging compromised credentials for initial entry and then exploiting internal services for further propagation. The presence of such vulnerabilities in critical infrastructure components like managed switches poses significant risks to organizational security postures, potentially leading to data exfiltration, network monitoring bypass, or complete network compromise depending on the device's role within the topology.
Mitigation strategies must address both immediate remediation and long-term defense-in-depth measures. The primary solution is to apply vendor-provided firmware updates that patch the webBackupAction function by implementing proper input length validation before buffer concatenation. Administrators should ensure all DrayTek VigorSwitch models are updated to the latest stable release as soon as patches become available. In cases where immediate patching is not feasible, network segmentation policies should be enforced to restrict access to the management interfaces of these switches exclusively from trusted administrative subnets or jump hosts. Additionally, implementing strict input validation at any reverse proxy or web application firewall positioned in front of the device can help filter out malformed requests that attempt to exploit this buffer overflow condition before they reach the vulnerable service layer. Regular auditing of admin account usage and enforcing multi-factor authentication for management interfaces further reduces the risk surface associated with credential-based exploitation vectors.