Re: Protocol Anomaly Detection IDS

From: Frank Knobbe (
Date: 02/11/03

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    From: Frank Knobbe <>
    Date: 11 Feb 2003 14:17:17 -0600

    On Mon, 2003-02-10 at 20:04, Martin Roesch wrote:
    > Just as an FYI, Snort can do protocol anomaly detection, through it's
    > rules-based engine, it's decoder and in its preprocessors. Protocol
    > anomalies mean different things to different people, of course, so it
    > depends on what you're really looking for.
    > People commonly think of Snort as a "signature based" IDS only, it's
    > actually capable of a lot more than that...

    In addition, besides signatures and protocol anomaly, Snort can also be
    used as a behavioral IDS. I have a habit of stressing the fact that
    after a Snort install/setup in your network, one should strive to craft
    additional Snort rules that define abnormal traffic, such as a web
    server establishing connections to the outside, etc. Snort is very
    capable of detecting abnormal traffic that way, and through it's
    detailed logging can give you clues to what's going on).

    Case in point: Just the other day, an engineer of a network vendor set
    up a laptop on the perimeter of a company to do some maintenance, and
    left the laptop hooked up overnight. Unfortunately, it was running an
    anonymous-writable FTP server. Companys signature based IDS didn't
    complain, but company's statistical IDS alerted to an FTP server which
    wasn't of much concern to the company since they knew that this IP was
    used by that laptop. Our Snort based appliance however picked up on the
    fact that there was a) an abnormal, rogue FTP present, and b) that that
    laptop was receiving parts of a Harry Potter movie in AVI form :)
    indicating an unsecure system (which our test confirmed).

    So, Snort is not just a signature and anomaly based IDS, it is also a
    behavioral IDS.