CVE-2026-71941 in VigorSwitch G2540xs
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a buffer overflow vulnerability in the diag_logmail function. The vulnerability is caused by concatenating multiple smtpReceiver email addresses into a fixed-size buffer without checking the remaining buffer size. 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.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/24/2026
The identified security flaw resides within the diag_logmail function of multiple DrayTek VigorSwitch models and represents a classic buffer overflow vulnerability stemming from improper input validation. The core technical issue arises when the system attempts to concatenate multiple SMTP receiver email addresses into a fixed-size memory buffer without performing adequate bounds checking on the remaining available space. This lack of boundary verification allows an attacker who provides crafted, excessively long input strings to write data beyond the allocated limits of the stack or heap segment where this buffer resides. In network infrastructure devices such as managed switches, functions responsible for logging and email notification are critical components that handle user-supplied configuration parameters directly in memory without sufficient sanitization, creating a direct path for memory corruption attacks when administrative interfaces process these inputs.
From an operational perspective, the exploitation of this vulnerability presents two distinct threat vectors depending on the attacker's objective and the specific architecture of the embedded operating system. The most immediate impact is a denial of service condition where the overflow corrupts critical control data such as return addresses or function pointers, causing the switch to crash or reboot unexpectedly. This disrupts network connectivity for all devices connected to the affected ports, leading to significant downtime in enterprise environments that rely on these switches for stable infrastructure operations. However, given that buffer overflows often allow for arbitrary code execution if memory layout can be manipulated correctly, a sophisticated attacker could potentially achieve remote command execution with the privileges of the compromised service process. This would grant full control over the network device, allowing for further lateral movement within the internal network or use as a pivot point for broader attacks against other systems on the same subnet.
The exploitation prerequisites significantly influence the risk profile and attack complexity associated with this vulnerability. Specifically, successful exploitation requires valid administrative credentials for the device's web management interface. This constraint classifies the threat primarily as an insider threat scenario or a result of credential compromise through phishing, brute force attacks against weak passwords, or theft of session tokens. While it is not remotely exploitable without authentication, the presence of such high-impact vulnerabilities in devices that often have default credentials enabled or are exposed to internal networks with varying levels of access control makes them attractive targets for attackers who have already gained a foothold within the perimeter. The requirement for administrative access means that robust identity and access management policies are the primary defense against this specific exploit path, rather than network-level filtering alone.
To mitigate these risks, organizations must implement strict input validation mechanisms on all configuration parameters passed to internal logging functions, ensuring that string lengths are checked before concatenation operations occur. From a defensive posture perspective, immediate patching of the DrayTek VigorSwitch firmware is essential if vendor-provided updates addressing this buffer overflow are available. In environments where patches cannot be applied immediately, network segmentation should be enforced to restrict administrative access to these devices only from trusted management stations using strong multi-factor authentication protocols. Additionally, enabling detailed logging and monitoring for unusual login attempts or configuration changes can help detect potential credential theft that precedes exploitation of such vulnerabilities.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-120, which describes buffer copy without checking size limits, a fundamental error in systems programming where the programmer assumes input will always fit within allocated memory spaces. Furthermore, from an adversary tactics perspective, this flaw relates to ATT&CK technique T1546, specifically Event Triggered Execution or components related to privilege escalation via local exploits if command execution is achieved. The scenario also reflects CWE-798, which covers the use of hard-coded credentials often found in such devices that facilitate initial access for attackers seeking administrative privileges before attempting deeper exploitation like this buffer overflow. Addressing these vulnerabilities requires a combination of secure coding practices during firmware development and rigorous operational security measures including regular credential rotation and least privilege enforcement for network management interfaces.