RE: DOCSIS vulnerability

[Justin Ellison <justin () techadvise com>]

I think you misunderstood his post.  These vendors have allowed him to
spoof the tftp server.  He's not hacking the ISP's tftp server, he's
creating his own files, placing them on his PC, and spoofing the ip of
the ISP's tftp server.  This is a vendor problem, because they should
only allow the tftp request to complete on the RF interface, not the
ethernet...

Justin

On Tue, 2002-03-12 at 04:49, Rense Buijen wrote:
> 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
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