An attacker who has obtained valid administrative credentials for the web interface can supply specially crafted inputs to these fields. By exceeding the expected buffer size, the attacker can cause the service to crash, resulting in a denial-of-service (DoS) condition, or potentially achieve arbitrary command execution on the target device. This vulnerability highlights the importance of restricting access to administrative interfaces and monitoring for anomalous configurations on edge networking equipment.

Impact

Successful exploitation of this vulnerability could lead to a complete compromise of the affected DrayTek VigorAP units, allowing attackers to persist within the network environment or disable critical wireless infrastructure. The vulnerability affects multiple VigorAP models globally. The requirement for administrative credentials limits the attack surface to those who have already gained unauthorized access to management accounts, but significantly escalates the impact of such access.

Recommendation

• Monitor web management interface logs for repeated or unusually formatted POST requests to the setLan function.
• Audit administrative account access and enforce multi-factor authentication (MFA) to mitigate the risk of credential theft required for exploitation.
• Check the official DrayTek support portal for firmware updates addressing CVE-2026-71911 and apply them to all exposed VigorAP devices.