Re: HOME_NET, EXTERNAL_NET, ipvar unwanted triggered rules

[David Smith <DSmith () smhcems org>]

alert udp $EXTERNAL_NET any -> $HOME_NET 53 (msg:"ET POLICY DNS Update From External net"; byte_test:1,!&,128,2; 
byte_test:1,!&,64,2; byte_test:1,&,32,2; byte_test:1,!&,16,2; byte_test:1,&,8,2; 
reference:url,doc.emergingthreats.net/2009702; classtype:policy-violation; sid:2009702; rev:5;)

This alert is being triggered each time a dns request is happening between to machines with the $HOME_NET subnets

Thanks for the quick reply
-----Original Message-----
From: Al Lewis (allewi) [mailto:allewi () cisco com] 
Sent: Friday, June 9, 2017 11:39 AM
To: David Smith <DSmith () smhcems org>; snort-users () lists sourceforge net
Subject: Re: [Snort-users] HOME_NET, EXTERNAL_NET, ipvar unwanted triggered rules

Hello,

        Do you have any example traffic?

Albert Lewis
ENGINEER.SOFTWARE ENGINEERING
SOURCEfire, Inc. now part of Cisco
Email: allewi () cisco com 








On 6/9/17, 12:32 PM, "David Smith" <DSmith () smhcems org> wrote:

> Members,
>
> ENV: Ubuntu 16.04, Snort V 2.9.9.0, Barnyard2 V 2.1.14, PulledPork 
> 0.7.3, BASE 1.4.5
>
>
> Snort rules, pulled in from PulledPork are being triggered from addresses within the defined HOME_NET as if they are 
> part of the EXTERNAL_NET, which is causing unwanted alerts.
>
> Snort.conf:
> ipvar HOME_NET [192.168.1.0/24,192.168.3.0/24] ipvar EXTERNAL_NET 
> !$HOME_NET
>
> Rule example:
> alert tcp $EXTERNAL_NET any -> $HOME_NET 53.........
>
> Can't find anything in docs or web that has solved this issue for me.    Thoughts or ideas?
>
> Thanks!
>
> Dave Smith
>
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