Reading a chapter in a book on data and computer communications, it goes over the statistical multiplexing used for cable modems to communicate with the headend scheduler that is in a box owned by the cable company.
The modems send requests to the scheduler for a timeslot to upload data in, and during that timeslot (and frequency slot), they upload data.
It seems like a fairly obvious hack or glitch could arise where a cable modem’s firmware is hacked to not care about timeslots, and it would just spam the network with garbage. This would prevent the upload signals from the other cable modems on the network from getting through, and I don’t see why it wouldn’t cause a failure of that section of the whole network. Everyone’s internet would go out, for however many households are sharing the same headend.
They use frequency filters to separate out the television signals, which means at least the TV would continue to work, I think.
The way this could be prevented is if the cable modem has many of these rules for timeslots defined in hardware, so it cannot be tampered with. This, however, would also preclude anyone being able to fix errors after shipping the retail modems.
It’s easy to find information online about uncapping a cable modem (what your hack is called), but I’ve not found or ever heard anything about uncapped modems causing any problems for anyone except the uncappers, who can expect to be dropped by their ISP when they’re caught.
Anyway, I haven’t found any evidence that uncapping has ever lead to a denial of service attack, distributed or otherwise. ISPs are apparently on-the-ball enough to kill misbehaving modems before they cause too many problems. That, or uncappers are so paranoid about getting caught they keep a really low profile and don’t use any extra bandwidth, which raises the question of why they uncapped their modems in the first place.
What would be the motive for doing this? If I understand the OP, by hacking a cable modem somebody could bring down their own internet connection, together with that of other people in the neighboring area that happen to use the same ISP? It does nor seem like something someone would want to do, even if they hate their neighbors. Alternatively, maybe someone a good deal more ingenious could remotely hack into your modem and bring down your connection and those of your neighbors. But, again, why?
As i understand it, this is not what DDOS attacks are normally about. Those are normally against particular web sites, and the servers that host them, and are aimed at harming, or, at least, protesting against, the companies and governments who control the sites in question. This is something very different from attacking the internet connections of individual consumers.