Certain D-Link devices have a hardcoded Alphanetworks user account with TELNET access because of /etc/config/image_sign or /etc/alpha_config/image_sign. This affects DIR-600 B1 V2.01 for WW, DIR-890L A1 v1.03, DIR-615 J1 v100 (for DCN), DIR-645 A1 v1.03, DIR-815 A1 v1.01, DIR-823 A1 v1.01, and DIR-842 C1 v3.00.
CVE Vulnerability