CVE-2026-71942 in VigorSwitch
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a buffer overflow vulnerability in the mail_mailalert 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.
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Analysis
by VulDB Data Team • 08/24/2026
The identified vulnerability resides within the mail_mailalert function of multiple DrayTek VigorSwitch models and represents a classic buffer overflow condition resulting from improper input validation. The core technical flaw stems from the system concatenating multiple SMTP receiver email addresses into a fixed-size memory buffer without performing adequate bounds checking on the remaining available space. When an administrator configures alerting settings through the web management interface, the application aggregates these recipient addresses and writes them directly to the stack or heap location allocated for this purpose. Because there is no mechanism to verify that the total length of the concatenated string fits within the predefined buffer limits, excessively long inputs will overwrite adjacent memory regions. This overwriting corrupts critical data structures such as return addresses, frame pointers, or function pointers, which fundamentally alters the control flow of the executing process.
From a threat modeling perspective, this vulnerability is categorized under CWE-120: Buffer Copy without Checking Size of Input (Classic Buffer Overflow). The lack of boundary checks allows an attacker to manipulate memory contents beyond their intended limits. While exploitation requires valid administrative credentials for the device's web management interface, which significantly raises the barrier to entry compared to unauthenticated attacks, it does not eliminate the risk entirely. Insider threats or compromised admin accounts can leverage this flaw to destabilize the network infrastructure. The operational impact is primarily a denial of service, as memory corruption typically causes the affected process or the entire switch firmware to crash, resulting in loss of connectivity and management capabilities for connected devices. However, depending on the specific architecture and compiler protections enabled during firmware compilation, an attacker might also achieve arbitrary code execution by carefully crafting the overflow payload to overwrite function pointers with shellcode addresses, thereby gaining full control over the network device.
This vulnerability aligns with MITRE ATT&CK technique T1059: Command and Scripting Interpreter if exploitation leads to remote command execution, or more broadly under lateral movement vectors where a compromised switch could be used as a pivot point within the internal network segment. The requirement for administrative access places this in the context of privilege abuse rather than initial network intrusion, highlighting that robust identity and access management is critical even when physical security controls are present. Defenders must recognize that local configuration interfaces often expose complex parsing logic vulnerable to such memory safety errors if not rigorously tested during firmware development cycles.
Mitigation strategies should focus on immediate patching by DrayTek for affected VigorSwitch models, ensuring that the vendor addresses the buffer size validation in the mail_mailalert function. In the interim, network segmentation policies should restrict access to the management interface of these switches to a highly secured administrative subnet with multi-factor authentication enabled to reduce the likelihood of credential compromise. Additionally, input filtering rules on any intermediate proxies or firewalls monitoring HTTP traffic to the device could potentially detect and block excessively long email address strings before they reach the vulnerable application logic. Long-term remediation requires adopting secure coding practices that enforce strict length checks and use safe string handling libraries that prevent buffer overflows from occurring in embedded network equipment firmware updates.