From: Jim Brown (jpbsixshooter.v6.thrupoint.net)
Date: Sat Jan 03 2004 - 18:10:46 CST

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* Paul Schmehl <paulsutdallas.edu> [2004-01-01 01:11]:
> ----- Original Message -----
> From: "Jeff Kell" <jeff-kellutc.edu>
> To: "Brice B" <nestaiceburg.net>
> Cc: <chris.northroppo.state.ct.us>; <snort-userslists.sourceforge.net>
> Sent: Wednesday, December 31, 2003 8:38 PM
> Subject: Re: [Snort-users] SUMMARY, CyberKit 2.2 Ping, its driven me Nuts..
> >
> > Can anyone verify the [non]existance of a difference between the
> > Cyberkit and Nachi pings? Not having Cyberkit myself, I can only
> > address Nachi. The frame is 106 bytes on the wire, 92 bytes in the IP
> > packet, and 64 bytes of 0xaa in the ICMP data payload.
> >
> > If Cyberkit is anything but 64 bytes of 0xaa payload, perhaps a new,
> > Nachi-specific rule is called for.
> >
> Here's the rule I wrote, which I've posted to the list several times. It
> uses thresholding and triggers one alert per minute. If you get *any*
> alerts with this rule, I *guarantee* you it's a machine infected with Nachi
> or a new variant of Nachi.
>
> # This rule is for tracking Nachi infections
> alert icmp $HOME_NET any -> any any (msg: "ALERT!!! NACHI Infection!!";
> content: "|aaaa aaaa aaaa aaaa aaaa aaaa aaaa aa
> aa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa
> aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa|";
> dsize:64; itype: 8; icode: 0; threshold: type both, track by_src, count
> 1000, seconds 60; classtype:trojan-activity; si
> d: 10000008; rev: 4;)
>
> The usual rules apply. This must be either all on one line or properly
> "escaped", so you'll have to fix it if you copy and paste. Note that this
> rule *only* triggers for internal infections, *not* for infected machines on
> $EXTERNAL_NET, so you need to edit it appropriately for what you are looking
> for on your network. I.e. change $HOME_NET to any if you want to catch
> *all* infections or $EXTERNAL_NET if you want to catch *incoming*
> infections.
>
> Paul Schmehl (paulsutdallas.edu)
> Adjunct Information Security Officer
> University of Texas at Dallas
> http://www.utdallas.edu/ir/

I'm curious about your threshold count of 1000 per minute. I've only
seen activity on the order of 12-15 messages/second on a 'blast'
with several seconds between blasts. This wouldn't get me to
1000 in one minute for most minutes.

What are your stats? Are you seeing more than 15 messages/second?

Best Regards,
jpb
===

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