Buffer Overflow in DrayTek VigorSwitch via SMTP Email Handling

Executive Summary

CVE-2026-71941 is a buffer overflow vulnerability in multiple DrayTek VigorSwitch models. It occurs in the diag_logmail function where the system concatenates multiple SMTP email addresses into a fixed-size buffer without checking the remaining space. This flaw allows a remote attacker with administrative credentials to trigger a buffer overflow, potentially causing a denial of service or executing arbitrary commands.

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Detection Guidance

To detect this vulnerability, check if your DrayTek VigorSwitch device is running firmware versions below the specified thresholds for affected models. Log in to the web management interface and inspect the diag_logmail function for improper email address concatenation handling. No specific commands are provided in the resources, but monitoring for crashes or unusual behavior in the SMTP email handling process may indicate exploitation.

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Impact Analysis

An attacker with administrative access could exploit this to crash the device, disrupting network operations. In severe cases, it may allow arbitrary command execution, enabling full control over the affected switch. This could lead to network downtime, data breaches, or unauthorized access to connected systems.

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Compliance Impact

This vulnerability could lead to unauthorized access or data breaches, violating GDPR's integrity and confidentiality requirements. For HIPAA, it may compromise protected health information if network devices are affected. Compliance failures could result in legal penalties, fines, or reputational damage.

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Mitigation Strategies

Immediately update the firmware of all affected DrayTek VigorSwitch models to versions that address this vulnerability. Ensure administrative credentials for the web management interface are strong and not shared. Disable unnecessary SMTP email logging features if possible. Monitor network traffic for unusual activity related to email handling on these devices.

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