This is the continuation of a write-up/tutorial-mixture on how to Reverse Engineer a patch with the ultimate goal of writing a Metasploit module for the found vulnerabilites.
I'll explain all that by taking the example of a patch that was released for the Fritz!Box devices, a widespread (at least in Germany/Europe) DSL-Router series in February 2014.

This tutorial/write-up illustrates the path from diffing the firmware versions and finding the interesting files via reverse engineering the patch through to finally writing an exploit (a Metasploit module) for the MIPS-based DSL-Router series by AVM.
Almost every Fritz!Box device (including WLAN-Repeaters) with a market share of ~60% in Germany is/was affected by this bug - patches were released between February 7th and 28th.