Snort mailing list archives

RE: detect that shouldn't be detected!


From: "Daniel Lopez" <dlopez () tct hut fi>
Date: Fri, 2 Aug 2002 11:43:13 +0300

Well, I went to check my "alert" file generated by the -A fast option.
This is the line that I got:

08/01-17:12:45.525894 [**] [113:2:1] spp_frag2: Teardrop attack [**]
{UDP} 10.50.1.130 -> 10.50.0.160

So, it seems it detects the Teardrop attack when it goes from my home
network to the external network.
Any idea? :-/


-----Original Message-----
From: Tom Sevy [mailto:tsevy () epx com]
Sent: Friday, August 02, 2002 2:54 AM
To: 'Daniel Lopez'
Subject: RE: [Snort-users] detect that shouldn't be detected!


I am not familiar with the 'tear' DoS, but if it is
monitoring UDP as it
indicates in the rule, is it possible that you are being
alerted by the udp
response?

-----Original Message-----
From: Daniel Lopez [mailto:dlopez () tct hut fi]
Sent: Thursday, August 01, 2002 7:03 PM
To: Tom Sevy
Subject: RE: [Snort-users] detect that shouldn't be detected!


Yes, but my HOME_NET is still set to 10.50.1.0/24. So, even if my home
network address is included in the EXTERNAL variable because I'm using
any, I'm launching the attack from 10.50.1.x -> 10.50.0.X

10.50.0.x is not an IP address that belongs to my Home network.
Am I still missing something? :-/


That is right.  Because 10.50.1.0 is included in your
EXTERNAL network
(any).

Try changing EXERNAL_NET to !$HOME_NET


-----Original Message-----
From: Daniel Lopez [mailto:dlopez () tct hut fi]
Sent: Thursday, August 01, 2002 4:49 PM
To: snort-users () lists sourceforge net
Subject: [Snort-users] detect that shouldn't be detected!


Hello,

Currently, I'm doing some tests on Snort. I'm using two LANs. One
recreates the External network. The network address is:
10.50.0.0/24.
The second LAN is my home network. The network address is:
10.50.1.0/24
They are interconnected via a router. I wanted to be able to
get attacks
going from the External network to my Home network, and
attacks going
from my Home network to the other computers in my Home network.
The SNORT box is in the home network. Computers and SNORT box are
connected through a HUB. I configured the HOME_NET and EXTERNAL_NET
variables as follows:

HOME_NET 10.50.1.0/24

EXTERNAL_NET any

However, when I launch an attack (Teardrop, NewTear) from my home
network to the external network, SNORT detects it!! If I look the
Teardrop rule, it is written this way:

[...] $EXTERNAL_NET -> $HOME_NET [...]

Thus, it only will be applied for traffic that goes from the
External_Net to the Home_Net!
I don't understand how it can detect it if the attack goes
from my home
network to the external network. Did I miss something?

Thanks in advance for your help!
Daniel Lopez




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