The Praetorian security blog has a very detailed and well-written blog post of a MIPS-based system, showing/discussing multiple tools (BowCaster, QIRA, BinWalk, Radare, …). And there is a Part 2 in the works!
Reversing and Exploiting Embedded Devices: The Software Stack (Part 1)
Over the course of the past few months I’ve been traveling around educating people on exploiting embedded devices. My slides alone aren’t able to provide enough information, so I wanted to write everything out for people to digest online. The following blog post is “Part 1”, which will introduce the reader to the software side of embedded devices. I decided to cover software first since most flaws reside within the software stack, ranging from binary applications to drivers. Part 2 will cover the Hardware stack with a focus on educating the reader on how JTAG actually works and how to leverage Hardware modifications to either bypass password protections or to extract secrets that may be baked into the targeted device. […]
https://www.praetorian.com/blog/reversing-and-exploiting-embedded-devices-part-1-the-software-stack
Firmware Security 