JaY’s Tech Tips: Hacking the Arris CM820 Cable modem


 Hello All.. Been a while but I have a minute of free time to release a Quick article on the art of device hacking.

The victim is a Arris Cable modem.. A pretty decent device that I purchased at a local trade it for 5$ in hopes of using it at my lady friends house.. Well after finding out that someone sold it to trade it when they decided to not pay their bill, I decided to not make it a total loss and do a quick article on the art of adding a serial port to get to the command line..


The exact model number and cmac address is worthless so I didn’t even bother blurring it out.


So We first want to get into the device so pop off the rubber feet and unscrew the case.. We will of course want to keep the power  off during this process as it is high voltage.


High Quality soldier masks and pretty nice power supply setup.  Good job. We need to now locate the serial interface. Usually 4 hols on the board. Pointed out in the picture below.   Time to put in some jumper posts and solder iron hackery begins. Muhahaha…  

A little messy but what do you want.. its hacking we don’t care.. hehe..

(probly should of turned the iron down to 450F instead of 800F)


Time to hook up a shifter cable (3.3v serial to 5v serial cable ebay for like 5$)

Pin out starting from the back of the modem to front is Ground, Receive, transmit, blank

Fire up Putty hook it to serial port COM * (whatever your shifter came up as)

Time for boot..


And we are in!!!

Basically the cable modem is a linux device. The command prompt is locked out so maybe next time we’ll work on that through the other port you see.. That is a JTAG port. It will be fun.

Happy hacking


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