CVE-2026-71911: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') in DrayTek Corporation VigorAP 918R

CVE-2026-71911 describes a classic buffer overflow vulnerability in multiple DrayTek VigorAP models, specifically in the setLan function. The flaw arises from the lack of input size validation when copying data into lanVlanId0, lanIp, and lanNetmask fields. An attacker with administrative access to the device's web management interface can supply crafted input to trigger this overflow, potentially causing denial of service or executing arbitrary commands on the device.

Successful exploitation can result in denial of service or arbitrary command execution on affected DrayTek VigorAP 918R devices. However, exploitation requires valid administrative credentials, limiting the attack surface to authorized users.

No official patch or remediation guidance is currently available. Users should monitor the vendor's advisories for updates. Since exploitation requires administrative access, restricting and monitoring administrative credentials and access to the device's management interface is recommended as a precautionary measure.