RE: frag3 alerts

["Drew Burchett" <DrewB () united-systems com>]

Well, I'm pretty sure I've got that set right.  The host is running Suse
Linux 10.0 and I've got the configuration set to:

preprocessor frag3_engine: policy linux bind_to 65.241.66.12

That seemed to be how I should have it set according to the chart in
README.frag3.

Drew Burchett
United Systems & Software
http://www.united-systems.com
Phone:  (270)527-3293
Fax:     (270)527-3132


> -----Original Message-----
> From: Joel Esler [mailto:joel.esler () sourcefire com]
> Sent: Monday, May 22, 2006 1:31 PM
> To: Drew Burchett
> Cc: snort-users () lists sourceforge net; rmkml
> Subject: Re: [Snort-users] frag3 alerts
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Of course.  Frag3 is target based (tuned to the OS) of your machine.
> Therefore you need to create an entry in your snort.conf specifically
> tuned to the OS of your DNS server (and any other host on your
network)
> If you need further help, feel free to email the list or me
personally,
> however, please review the examples in the snort.conf under the frag3
> heading.
>
> Joel Esler
>
> Drew Burchett wrote:
> > From examining the packet capture, I?ve determined that the
?offending?
> > traffic is an NXDomain response from a valid root server.  It?s
being
> > caused by doing reverse lookups on spam email.
> >
> >
> >
> > However, the question remains, is there any way I can fine tune the
> > frag3 preprocessor to avoid these false positives?
> >
> >
> >
> > Drew Burchett
> >
> > United Systems & Software
> >
> > http://www.united-systems.com
> >
> > Phone:  (270)527-3293
> >
> > Fax:     (270)527-3132
> >
> >
> >
> > * From: * snort-users-admin () lists sourceforge net
> > [mailto:snort-users-admin () lists sourceforge net] *On Behalf Of *Drew
> > Burchett
> > *Sent:* Monday, May 22, 2006 11:18 AM
> > *To:* snort-users () lists sourceforge net
> > *Subject:* [Snort-users] frag3 alerts
> >
> >
> >
> > I am seeing a lot of frag3 Fragmentation overlap alerts with my DNS
> > server as the destination and a source address that reverses to a
root
> > server.  When examining the packets, the traffic seems to be valid
DNS
> > traffic, although it has nothing to do with any domains that I host.
Is
> > this some sort of attack, or is it valid traffic that is throwing
false
> > positives?  If it is a false positive, is there any way I can
fine-tune
> > the frag3 preprocessor to avoid these?
> >
> >
> >
> > Drew Burchett
> >
> > United Systems & Software
> >
> > http://www.united-systems.com
> >
> > Phone:  (270)527-3293
> >
> > Fax:     (270)527-3132
> >
> >
> >
> >
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recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or 
distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and 
destroy all copies of the original message.

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