Get the Whitepaper called From Patched to Pwned – Attacking Xerox’s Multifunction Printers Patch Process. In this paper the author discusses the step by step process around how to gain root level access to high end Xerox MFP devices, how the firmware signing process works, and how to protect yourself from this attack.
You can download it from the following link: https://packetstormsecurity.com/files/download/120570/Xerox_hack.pdf
Source: https://packetstormsecurity.com/files/120570/Attacking-Xeroxs-Multifunction-Printers-Patch-Process.html