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Re: writing SNORT rules
From: Chris Green <cmgreen () UAB EDU>
Date: Tue, 2 Dec 2008 10:47:53 -0600

Write the rules out using only your CIDR notation and you get:

(assuming you have SSH_PORTS defined)

 

alert tcp !137.165.0.0/16 any -> 137.165.224.0/24 22 (flow:stateless;
flags:S,12; msg: "test"; sid: 1234125);

 

Where are you testing from? On campus?

 

From: The EDUCAUSE Security Constituent Group Listserv
[mailto:SECURITY () LISTSERV EDUCAUSE EDU] On Behalf Of Peter Charbonneau
Sent: Tuesday, December 02, 2008 10:14 AM
To: SECURITY () LISTSERV EDUCAUSE EDU
Subject: [SECURITY] writing SNORT rules

 

Good morning 

 

I have written 3 "quick and dirty" SNORT rules and am trying to follow
the write/test/write/test/write/test/write/test 

 

Unfortunately even the first test isn't working.  I never see the alert
message for these rules in my alert log.  Is there some other directive
in the snort.conf file that could be precluding these stateless "hits"
from being processed in some way?

 

If you have any responses, we should probably take this off-line to keep
the list from being clogged, unless, of course, this is a "class"
problem for all first time rule writers.  I think it's something stupid,
but I just can't see it.

 

 

These are the simplest rules I could think of with the ongoing process
of modifying them for my final needs.  My ultimate goal is to be able to
grep the alert file for this LOCAL message and grab the timestamps; I
want come up with a way to sanity check the duration of established ssh
sessions to compare against host machine log files.

 

Here are the rules:

 

[root () netsniff emerging]# cat /usr/local/etc/rules/local.rules

# $Id: local.rules,v 1.13 2005/02/10 01:11:04 bmc Exp $

# ----------------

# LOCAL RULES

# ----------------

#

alert tcp $EXTERNAL_NET any -> $NETSYS_NET $SSH_PORTS (flow:stateless;
flags:S,12; msg: "LOCAL Connection attempt -- NetSys asset on port 22";
sid: 2008001;)

alert tcp $EXTERNAL_NET any -> $NETSYS_NET $SSH_PORTS (flow:stateless;
flags:F,12; msg: "LOCAL Connection termination -- NetSys asset on port
22"; sid: 2008002;)

alert tcp $EXTERNAL_NET any -> $NETSYS_NET $SSH_PORTS (flow:stateless;
flags:R,12; msg: "LOCAL Connection reset -- NetSys asset for port 22";
sid: 2008003;)

[root () netsniff emerging]# 

 

The variables EXTERNAL_NET, NETSYS_NET, SSH_PORTS are all defined:

 

var HOME_NET 137.165.0.0/16

var NETSYS_NET 137.165.224.0/24

var EXTERNAL_NET !$HOME_NET

 

 

RULE_PATH is defined as var RULE_PATH /usr/local/etc/rules

 

 

Here is the portion of the snort.conf file that "includes" the
local.rules file:

 

# 

# Please read the specific include file for more information and

# README.alert_order for how rule ordering affects how alerts are
triggered.

#=========================================

 

include $RULE_PATH/local.rules

# include $RULE_PATH/bad-traffic.rules

include $RULE_PATH/exploit.rules

 

 

I have stopped and restarted snort with the same command line I always
use:

 

snort -A full -i eth3 -N -K none -c /usr/local/etc/snort.conf -D

 

PeteC

 

 

Peter Charbonneau

Sr. Network and Systems Administrator

Williams College

(413) 597-3408 (office)

(413) 822-2922 (cell)

 





 


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