Re: ISP reconfiguring cable modem?

oni_at_omgsoleetyes.com
Date: 05/29/04

  • Next message: Hugo Deckx: "RE: Computer Forensics Consulting" 
    Date: Fri, 28 May 2004 21:19:13 -0400
To: Paul Kurczaba <paul@myipis.com>

    Cable modems are programmed to grab a configuration file via TFTP (if
    I'm not mistaken) from the HE (head end) upon gaining sync.

    I work as a tech support rep for a local cable internet provider. We
    shut off modems all the time for abuse such as spam, or virii infections.

    We use a web-based OS to disable and enable, and reset modems. All we
    do flip a switch to disable the modem, the OS writes a new config file
    for that one customer to tell the modem to not transmit any traffic when
    this config file is loaded onto the modem. After the config file is
    ready, we send a remote command to the modem telling it to reboot, once
    it reboots, gains sync, and gets the new (modified) config file it no
    longer transmits any traffic in or out.

    Since the modem grabs a new config file every time it sync's up to the
    HE, and we have the ability to reset modems remotely.. We can disable
    abusers internet traffic as needed, and not make any perm. changes to
    the modem it self.. Thus if they can take their self-owned modems off
    of our system while we have them disabled, plug into another cable inet
    provider, and surf away because the other ISP is giving that modem a new
    fresh config file when it sync's up.

    Thats the basic gist of how the DOCSIS standard works, and how cable
    modems don't need to be pre-configured by a cable internet provider like
    some adsl modems.

    The whole process is pretty secure. The point of failure would be with
    the interface the employees use however, which can be exploited if the
    ISP doesn't know how to secure itself properly.

    -Ben

    Paul Kurczaba wrote:

    >On this ZDNet article
    >(http://zdnet.com.com/2100-1107_2-5218720.html?tag=zdaresources), it
    >mentions that to help prevent spam, comcast could remotely reconfigure the
    >cable modem if it sees that user is sending out a bunch of spam. How is it
    >possible to remotely configure the cable modem? Would it be a TCP/IP or
    >cable signal that would reconfigure the modem? If it is TCP/IP, couldn't a
    >hacker screw up the modem? If it is a cable signal, what happens if the
    >cable user bought the modem at best buy or compusa (it wouldn't be ISP
    >specific)
    >
    >-Paul Kurczaba
    >
    >
    >
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    ---------------------------------------------------------------------------
    Ethical Hacking at the InfoSec Institute. Mention this ad and get $545 off
    any course! All of our class sizes are guaranteed to be 10 students or less
    to facilitate one-on-one interaction with one of our expert instructors.
    Attend a course taught by an expert instructor with years of in-the-field
    pen testing experience in our state of the art hacking lab. Master the skills
    of an Ethical Hacker to better assess the security of your organization.
    Visit us at:
    http://www.infosecinstitute.com/courses/ethical_hacking_training.html
    ----------------------------------------------------------------------------

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