On ORing net IAP-420(+) with FW version 2.0m a telnet server is enabled by default and cannot permanently be disabled. You can connect to the device via LAN or WiFi with hardcoded credentials and get an administrative shell. These credentials are reset to defaults with every reboot.
CWE-912 - Hidden Functionality
The software contains functionality that is not documented, not part of the specification, and not accessible through an interface or command sequence that is obvious to the software's users or administrators.