CVE-2026-71939 in VigorSwitch
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a buffer overflow vulnerability in the acl_general_setup Add ACE function. The vulnerability is caused by copying the name field into a fixed-size buffer without length validation. 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 DrayTek VigorSwitch series contains a critical security flaw within its network access control configuration module, specifically located in the acl_general_setup function responsible for adding Access Control Entry rules. This vulnerability stems from an improper memory handling mechanism where user-supplied input is copied into a fixed-size buffer without performing adequate length validation checks. The specific field affected is the name parameter used to identify or label the access control rule. When this data exceeds the allocated stack space, it results in a classic buffer overflow condition that corrupts adjacent memory regions including return addresses and saved frame pointers.
From an operational perspective, this vulnerability allows for significant disruption of network infrastructure services. An attacker who has obtained valid administrative credentials through phishing, credential stuffing, or other means can exploit this flaw to crash the management interface process, leading directly to a denial of service condition where switch configuration changes become impossible until a reboot occurs. More critically, given that modern embedded systems often utilize stack-based execution environments with predictable memory layouts, skilled attackers may leverage precise payload construction to overwrite function return addresses and redirect program flow. This capability enables the potential execution of arbitrary commands within the context of the vulnerable process, which typically runs with elevated privileges on the device's operating system.
The exploitation vector for this vulnerability is classified as remote but requires authentication, placing it in a specific threat category where insider threats or compromised administrative accounts pose the highest risk. The lack of input sanitization indicates a fundamental oversight in secure coding practices during the development of the web management interface backend logic. This aligns with Common Weakness Enumeration standard CWE-120 which describes buffer copy without checking size limits, and CWE-787 regarding out-of-bounds write access that leads to undefined behavior or code execution. The attack pattern corresponds to ATT&CK technique T1546.003 involving Event Triggered Execution via ACL modification if the overflow allows persistence mechanisms to be installed through command injection following successful exploitation.
Mitigation strategies must prioritize immediate patching of the firmware on all affected VigorSwitch models as soon as official updates are released by DrayTek. In environments where patches cannot be applied immediately, network segmentation should be enforced to restrict access to the management interface exclusively from trusted administrative subnets using firewalls or VLAN isolation. Additionally, implementing strict password policies and multi-factor authentication for administrative accounts reduces the likelihood of credential compromise that precedes exploitation. Security monitoring tools should also be configured to detect anomalous HTTP requests containing unusually long strings in configuration parameters which may indicate attempted buffer overflow attacks against the web management interface.