Re: Snort BPF.filter doesn't work

[James Lay <jlay () slave-tothe-box net>]

On 2014-07-08 12:38, Robert Millott wrote:
> Anyone else have any experience working with BPF Filters?I have
> followed all the directions I have been able to find and set up my
> filters, but a test rule I created continues to fire, even though the
> bpf filter should ignore that host entirely.
>
> Thank you
>
> On Thu, Jul 3, 2014 at 1:26 PM, Robert Millott
> <robm () millottandassociates com [9]> wrote:
>
> > unfortunately, my snort install is on a non-internet connected
> > network so I cant provide the .conf file.
> >
> > my command to start snort is:
> >
> > /usr/bin/snort -c /etc/snort/snort1.conf -G 0x11 --pid-path
> > /etc/snort/ --nolock-pidfile --daq pcap --dap-dir /usr/lib64/daq
> > --daq-mode passive -i enps50f0 -F /etc/snort/bpf.filter -D
> >
> > snort version is 2.9.6 GRE (Build 47)
> > host OS is 3.14.4 gentoo 
> >
> > Thanx for the help
> >
> > On Thu, Jul 3, 2014 at 1:19 PM, Nicholas Mavis (nmavis)
> > <nmavis () cisco com [8]> wrote:
> >
> > > Robert,
> > >
> > > Can you provide the following:
> > >
> > > * Copy of your snort.conf
> > > * The syntax in which you are starting Snort
> > > * What version of Snort are you using?
> > >
> > > -Nick
> > >
> > > From: Robert Millott <robm () millottandassociates com [4]>
> > > Date: Thursday, July 3, 2014 at 1:16 PM
> > > To: nmavis <nmavis () cisco com [5]>, snort-users
> > > <snort-users () lists sourceforge net [6]>
> > > Subject: Re: [Snort-users] Snort BPF.filter doesnt work
> > >
> > > Nick
> > >   Thanx for the suggestion. Unfortunately, same results.  The
> > > startup screen shows it reads the file, but the alert keeps
> > > showing up in my logs.
> > >
> > > On Thu, Jul 3, 2014 at 1:10 PM, Nicholas Mavis (nmavis)
> > > <nmavis () cisco com [7]> wrote:
> > >
> > > > Robert,
> > > >
> > > > Try the following without any additions:
> > > >
> > > > not host 192.168.1.1
> > > >
> > > > -Nick
> > > >
> > > > From: Robert Millott <robm () millottandassociates com [1]>
> > > > Date: Thursday, July 3, 2014 at 12:14 PM
> > > > To: "snort-users () lists sourceforge net [2]"
> > > > <snort-users () lists sourceforge net [3]>
> > > > Subject: [Snort-users] Snort BPF.filter doesnt work
> > > >
> > > > I am trying to filter some data.  I created a rule in my
> > > > misc.rules that I know will always fire, ie
> > > >
> > > > alert tcp any any -> 192.168.1.1 80 (msg:"my test rule"; sid:
> > > > 60999; rev:1)
> > > >
> > > > That rule fires constantly whenever I go to the website at
> > > > 192.168.1.1
> > > >
> > > > I then create a /etc/snort/bpf.filter that contains one line
> > > >
> > > > !(host 192.168.1.1)
> > > >
> > > > I then edited snort.conf and uncomment the bfp.filter line so it
> > > > reads
> > > >
> > > > config bpf_file: /etc/snort/bpf.filter
> > > >
> > > > When I run snort and watch /var/log/messages, the above alert
> > > > continues to fire.
> > > >
> > > > I also tried using it with the command line option of -F
> > > > /etc/snort/bpf.filter. This didnt work either.
> > > >
> > > > I also tried bpf.filter to read
> > > > (not host 192.168.1.1)
> > > > that didnt work either.
> > > >
> > > > When I start snort, I see the line that reads 
> > > >
> > > > Snort BPF Option:
> > > > !(host 192.168.1.1)
> > > >
> > > > and yet I still see my above test alert message in my
> > > > /var/log/messages.  
> > > >
> > > > Anyone know why the bpf.filter isnt filtering the data?
> > > >
> > > > --
> > > > Robert Millott
> > > > President, Millott and Associates
> > > > (443) 255-3588

Just pass it direct:

/usr/bin/snort -c /etc/snort/snort1.conf -G 0x11 --pid-path /etc/snort/ 
--nolock-pidfile --daq pcap --dap-dir /usr/lib64/daq --daq-mode passive 
-i enps50f0 not host 192.168.1.1

James

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