RE: DOCSIS vulnerability

["Rense Buijen" <Rense.Buijen () dct-mail com>]

Maybe your posts were rejected because this is very old news.
This is known for ages, I have such a cable modem and indeed you can get
the config file by TFTP; decode, alter, encode and upload it, but the
ISP's are not stupid and most of the time this is NOT how they cap your
cable modem, they throw traffic into a packeteer or use other methods to
squeeze your bandwidth.

All the info can be gathered by a tool like this:
http://www.weird-solutions.com/_bin/bootpq.exe

And a simple google search shows up hundreds of articles explaining how
you can "hack" DOCSIS cable modems, unfortunately (unless you have a
completely clueless provider) all these tricks wont work.

E.g: http://lists.wi2600.org/pipermail/2600/2001-October/008668.html

Which dates from October 2001.

(I tried it but my isp squeezes on the other end of the pipe, some
things that you can alter though is bypass restrictions of how many
computers could be connected right into the modem)

With kind regards,

Rense

-----Original Message-----
From: Matthew S. Hallacy [mailto:poptix () techmonkeys org] 
Sent: dinsdag 12 maart 2002 4:55
To: vuln-dev () securityfocus com
Subject: DOCSIS vulnerability

Hi,

Apparently this isn't bugtraq worthy (my posts weren't rejected, they
were simply
deleted), so I'll send it here.

---

Pre-ramble:

        I've been debating this for a while, but now I'm sufficiently
agitated by dishonest cable ISP's to post it.

Background:

        DOCSIS was created to be a standard for data over cable systems
so
that a cable modem that worked on one system would work just as well on
the
next, this brings down hardware costs, as well as training costs.
Basicly
you plug the cable modem in, it acquires a data path to the ISP's
hardware,
and sends a BOOTP request. The BOOTP reply that it recieves contains a
few
items, a syslog server, a tftp server, a time server, and a config file
to
download from the TFTP server. Until now everyone has claimed that it's
impossible to disrupt this, 6 months ago I found a way to.

Ramifications:

Everything from 'uncapping' your cable modem to being able to destroy
the cable network you're connected to, this is how cable companies
rate limit their customers, it's how they keep their customers
DHCP servers from replying to DHCP requests from other customers,
it's also how they block everything from netbios to web servers.
this is also the method used to restrict customers to a certain
number of IP addresses.

Details:

It's a simple attack, while the modem is booting it looks for the
address
of the TFTP server, simply assaign that address to your system and ping
the cable modem on its management address (usually 192.168.100.1). It
will
then connect to your machine to download the TFTP configuration file.

This is known to work on the following models:
Motorola (all models)
3Com Sharkfin
Toshiba PCX 1100

This is known to NOT work on these models:
RCA DCM235
3Com CMX



Copyright:
If you're redistributing this, keep it intact.
(c) 2002 Matthew S. Hallacy