Printer has become one of the essential devices in the corporate intranet for the past few years, and its functionalities have also increased significantly. Not only print or fax, cloud printing services like AirPrint are also being supported as well to make it easier to use. Direct printing from mobile devices is now a basic requirement in the IoT era. We also use it to print some internal business documents of the company, which makes it even more important to keep the printer safe. Nowadays, most of the printers on the market do not have to be connected with USB or traditional cable. As long as you are using a LAN cable connected to the intranet, the computer can find and use the printer immediately. Most of them are based on protocols such as SLP and LLMNR. But is it really safe when vendors adopt those protocols? Furthermore, many printers do not use traditional Linux systems, but use RTOS(Real-Time Operating System) instead, how will this affect the attacker? In this talk, we will use Canon ImageCLASS MF644Cdw and HP Color LaserJet Pro MFP M283fdw as case study, showing how to analyze and gain control access to the printer. We will also demonstrate how to use the vulnerabilities to achieve RCE in RTOS in unauthenticated situations.