D-Link DIR-2640 HNAP LoginPassword Authentication Bypass Vulnerability. This vulnerability allows network-adjacent attackers to bypass authentication on affected installations of D-Link DIR-2640 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the web management interface, which listens on TCP port 80 by default. A specially crafted login request can cause authentication to succeed without providing proper credentials. An attacker can leverage this vulnerability to bypass authentication on the system. . Was ZDI-CAN-19549.