CVE-2026-71938: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') in DrayTek Corporation VigorSwitch G2540xs

CVE-2026-71938 is a classic buffer overflow vulnerability in DrayTek VigorSwitch G2540xs devices. The vulnerability occurs due to unsafe copying of the portList field into a buffer that is too small within the switch_lan_gvrp function. A remote attacker with valid administrative credentials to the device's web interface can trigger this vulnerability by supplying crafted input, potentially causing denial of service or arbitrary command execution. The CVSS 4.0 score is 8.6, indicating high severity, with network attack vector, low attack complexity, no user interaction, and requiring high privileges.

Successful exploitation can cause denial of service or potentially allow execution of arbitrary commands on the affected device. However, exploitation requires valid administrative credentials, limiting the attack surface to authorized users.

No official patch or remediation is currently confirmed. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, restrict administrative access to trusted personnel only and monitor for suspicious activity on the management interface.