Xerox Workcentre firmware injection exploit

This PR is for the Xerox workcentre 56xx-57xx and 76xx-77xx series multifunction printer exploit. This exploit leverages the firmware upgrade process to execute bash commands on the device with root level privileges. 

Below is an example of the payloads available in the module:
![screen shot 2014-10-28 at 12 03 10 pm](https://cloud.githubusercontent.com/assets/6502552/4811698/1a5793f4-5ebc-11e4-9686-feb4a3156ae1.png)


Below is an example of the options available in the module with  payload "cmd/unix/reverse_bash" set.
Module options (exploit/test/xerox_mfp):
![screen shot 2014-10-28 at 12 01 12 pm](https://cloud.githubusercontent.com/assets/6502552/4811672/ee1dae18-5ebb-11e4-8450-ac3df35e3a59.png)

Steps to launch a reverse shell exploit against vulnerable Xerox Workcentre devices:
 
- [ ] set PAYLOAD cmd/unix/reverse_bash
- [ ] set RHOST to targeted Xerox devices IP address
- [ ] set RPORT to targeted Xerox devices jetdirect port number
- [ ] set LHOST to local host IP address for reverse shell to connect back to
- [ ] set LPORT to local host port number for reverse shell to connect back to 

Below is an example using the payload "cmd/unix/reverse_bash" to gain reverse bash shell with root privileges on a Xerox Workcentre 5735 multifunction printer.

![screen shot 2014-10-28 at 12 07 32 pm](https://cloud.githubusercontent.com/assets/6502552/4811826/f76c75ca-5ebc-11e4-94f4-e32a35e8144e.png)

Any question please contact me





Ok i have converted what was text over so its viewable. Just to points out the block is actually a firmware package build using Xerox dlm_maker tool. This header data plays a critical roll on how the Xerox device handles it. Most of the data in incorporated into the key signing process. only two lines can be altered without corrupting the key validation or the firmware execution process.
The first comment line allows us to inject our payload. The string "PraedaPWN2014" is an egg which we use to find the payload from print job files that land in the print spooler. When our firmware boot strap code runs is searches the print job files for that string when it finds it, it parses out the payload and passes the payload to a bash shell.

The second comment line must at a minimum contain the keyword "patch". Which is used by Xerox printer firmware process to determine what operation type to execute. So i removed the time stamp that was created by the xerox firmware tool dlm_maker.
This is generally why we originally left it as hex, cause most changes or alteration will corrupt the key validation process within the printer, rendering the firmware as invalid.

Its all changed now!