The CenturyLink C2000T router is a pretty capable little device that’s been saddled with some truly awful software. It’s currently unsupported by DD-WRT, which is unfortunate, because the hardware itself is pretty solid.
Getting root was so easy I’m not even sure if it qualifies as a hack, or if this was intended behavior.
First, follow CenturyLink’s guide for enabling telnet access to your router.
Then–and yes, it really is this easy–log in with the username and password you just set. You’ll be at what I assume is intended to be a Cisco IOS-style interface. (I didn’t use it long enough to find out.) Type ‘sh’, and you’ll be rewarded with a root BusyBox session.