[Snort-users] frag3 alerts

Joel Esler joel.esler at ...1935...
Mon May 22 11:39:02 EDT 2006


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How do you have the rest of the frag3 entries set?  Or is that the only
entry you have?

Joel

Drew Burchett wrote:
> 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 at ...1935...]
>> Sent: Monday, May 22, 2006 1:31 PM
>> To: Drew Burchett
>> Cc: snort-users at lists.sourceforge.net; rmkml
>> Subject: Re: [Snort-users] frag3 alerts
>>
> 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 at lists.sourceforge.net
>>>> [mailto:snort-users-admin at lists.sourceforge.net] *On Behalf Of *Drew
>>>> Burchett
>>>> *Sent:* Monday, May 22, 2006 11:18 AM
>>>> *To:* snort-users at 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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> --
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