On D-Link DIR-550A and DIR-604M devices through v2.10KR, a malicious user can forge an HTTP request to inject operating system commands that can be executed on the device with higher privileges, aka remote code execution.
On D-Link DIR-550A and DIR-604M devices through v2.10KR, a malicious user can use a default TELNET account to get unauthorized access to vulnerable devices, aka a backdoor access vulnerability.