D-link - Dir-456u Firmware - CRITICAL - CVE-2026-42376. The D-Link DIR-456U A1 device has a serious security flaw characterized by a hardcoded telnet backdoor. This backdoor allows an unauthenticated attacker on the local network to gain root access to the device. The device initializes a telnet daemon during boot, exposing a hardcoded username and password. This poses a significant risk, considering the device has reached End-of-Life status and will not receive any patches to mitigate this vulnerability.