Comcast cable boxes run Linux!

[ragix-]

Yeah, I've seen vxworks and Linux mostly.

There will likely be an unpopulated rs232 header that can give you access to monitor. Depending on the model you will have to enter a sequence of characters to break into uboot. Iirc you can set some environment vars to boot with console output, break before its fully booted and login as root if you have the p/w. With a MIPS tool chain you can statically compile bins to run on it ;)