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.
Credits
Lorenzo Bazzana and Marino Miculan of Università degli studi di Udine, Michele Codutti of Danieli Automation
