Snort Installation Notes

I installed this on a 32-bit CentOS 5.6 system, with MySQL as the output
backend for snort.


Install Snort

Snort v2.9+ use libpcap 1.0+. Unfortunately, CentOS 5.x still uses
v0.9.4. I tried (the hard way) to compile my own RPMs and stop swearing
at the screen. However, a gentleman by name Vincent Cojot has already
done some awesome

for all of us. Of course, the makers of Snort recommend that you compile
it and don’t vouch for Vincent RPMs. But I have shit to do.

mkdir snort; cd snort  
rpm -ivh *.rpm

Important: v2.9.0.5 RPMs have some
significant path-related issues when trying to find rulesets. I
recommend sticking with v2.9.0.4

Install Snort Rules

You’ll need to register on Snort’s website before you can download a
ruleset. New rulesets are released to subscribers ($$$) 30 days before
registered users (FREE!) can download them.

# The ruleset is a tarbomb  
mkdir snort-rules; cd snort-rules  
tar -xvzf snortrules-snapshot-2903.tar.gz  
cp etc/* /etc/snort/  
cp rules/* /etc/snort/rules/  
cp so_rules/precompiled/Centos-5-4/i386/* /etc/snort/so_rules/  
cp preproc_rules/* /etc/snort/preproc_rules/

Now we’re ready to bend Snort to our whim.

Set up the Snort user and group

The RPM should already set this up for you. If not,

[root@snort usr]# groupadd snort  
[root@snort usr]# useradd -g snort snort  
[root@snort usr]# id snort  
uid=505(snort) gid=506(snort) groups=506(snort)

You’ll then need to chown /var/log/snort.

Set up the MySQL database

Set up your database (call it “snort”) and user (also called “snort”)
and password (“PASSWORD”). Now load the schema:

mysql -uroot -p snort < /usr/share/snort-

Configuring Snort

Start editing /etc/snort/snort.conf (make a copy of the original
first!) Here are my modifications to the original file:

ipvar HOME_NET  
portvar SSH_PORTS [22,3232]  
portvar HTTP_PORTS [80,443,8080,9066]  
# These were relative  
var RULE_PATH /etc/snort/rules  
var SO_RULE_PATH /etc/snort/so_rules  
var PREPROC_RULE_PATH /etc/snort/preproc_rules  
# These were commented out  
include $PREPROC_RULE_PATH/preprocessor.rules  
include $PREPROC_RULE_PATH/decoder.rules  
include $PREPROC_RULE_PATH/sensitive-data.rules  
# Listed as /usr/local/lib when they were actually in /usr/lib  
dynamicpreprocessor directory /usr/lib/snort_dynamicpreprocessor/  
dynamicengine /usr/lib/snort_dynamicengine/  
dynamicdetection directory /usr/lib/snort_dynamicrules  
# Increased to 65535 to avoid startup errors (I don't know the full reason yet)  
preprocessor http_inspect: global iis_unicode_map 1252 compress_depth 65535 decompress_depth 65535  
# This was commented out; detects portscans!  
preprocessor sfportscan: proto  { all } memcap { 10000000 } sense_level { low }  
# MySQL connection params  
output database: alert, mysql, user=snort password=PASSWORD dbname=snort host=localhost  
output database: log, mysql, user=snort password=PASSWORD dbname=snort host=localhost

Then uncomment all the preprocessor rules includes.


Although the Snort config above looks like it should log everything to
your MySQL database, you’ll soon find that it doesn’t. Running the test
command in the section below will lead to Snort declaring that
everything’s peachy. It will create a single row in snort.sensor and
nothing else.

I wasted about 4 hours attempting to reconfigure Snort, reading through
the config file again, making sure my DB was okay. It was this post on
the Snort

that made my day. You basically open up /etc/sysconfig/snort and
comment out this stupid line:


That’s it. Restart snortd and Snort will now log to /var/log/snort
and your MySQL instance. Thanks “aline”!

IMPORTANT: Logging to custom logfiles

It took me 24 painstaking hours to figure this out. I can write a poem
on the frustration. Basically, Snort wouldn’t write to a logfile of my
choice and I didn’t know why. Turns out that I had to turn off binary
logs in /etc/sysconfig/snort:


If you don’t do this, Snort won’t care what you specify your unified2
logfiles to be; it will always write to snort.log.<timestamp>.

Test Run

Check your configuration with this:

/usr/sbin/snort -T -u snort -g snort -c /etc/snort/snort.conf

Using the -D flag will run snort in daemon mode and is not useful. If
everything looks OK,

[root@snort snort]# service snortd start  
Starting snort: Spawning daemon child...  
My daemon child 30815 lives...  
Daemon parent exiting                           [  OK  ]

Installing Oinkmaster

This downloads and updates rulesets on a cron job. You’ll need an
“Oinkcode” which you can procure from your account.

cd /opt  
wget -O - | tar -xvzf -  
ln -s oinkmaster-2.0 oinkmaster  
cd oinkmaster  
cp oinkmaster.conf oinkmaster.conf.original  
mkdir tmp backup.rules

Then edit the config file to specify URLs and oinkcodes:

url =<your code>/snortrules-snapshot-2900.tar.gz  
tmpdir = /opt/oinkmaster/tmp

I prefer keeping oinkmaster in /opt. For a trial run, I issue:

mkdir /tmp/snort  
/opt/oinkmaster/ -c -v -C /opt/oinkmaster/oinkmaster.conf -o /tmp/snort/

As a poor registered user, you have to wait 15 minutes between
downloads. If all’s well, you can now set a cron job with:

# Download new Snort rulesets every Friday at midnight  
0 0 * * 5 /opt/oinkmaster/ -C /opt/oinkmaster/oinkmaster.conf \  
          -o /etc/snort/rules/ -b /opt/oinkmaster/backup.rules  \  
          2>&1 | mail -s "snrt - oinkmaster"

Backs up rules, emails you everything on Friday at midnight. Awesome.

Using Barnyard to Spool Data

Preconfiguring Snort

Open up /etc/snort/snort.conf change this line:

output unified2: filename merged.log, limit 128, nostamp, mpls_event_types, vlan_event_types

to this:

output unified2: filename merged.log, limit 128

For some reason, barnyard2 will not work if you don’t do this. Now
comment out every other output declaration and restart Snort.

Installing Barnyard

Edit /usr/local/etc/barnyard2.conf. Here’s a diff of the original
(<) and my modifications (>):

< #config hostname: thor  
< #config interface:  eth0  
> config hostname:  
> config interface: eth0  
< #config show_year  
> config show_year  
< #config waldo_file: /tmp/waldo  
> config waldo_file: /var/log/snort/barnyard2.waldo  
< #config archivedir: /tmp  
> config archivedir: /var/log/barnyard2  
< output alert_fast: stdout  
> #output alert_fast: stdout  
> output database: log, mysql, user=snort password=PASSWORD dbname=snort host=localhost  
> output database: alert, mysql, user=snort password=PASSWORD dbname=snort host=localhost

Now set up the waldo file and a few folders:

mkdir /var/log/barnyard2  
chmod 666 /var/log/barnyard2  
chown snort:snort /var/log/barnyard2  
touch /var/log/snort/barnyard2.waldo  
chown snort:snort /var/log/snort/barnyard2.waldo

I highly recommend testing this configuration:

/usr/local/bin/barnyard2 -T -c /usr/local/etc/barnyard2.conf

Now start barnyard in daemon mode:

/usr/local/bin/barnyard2 -c /usr/local/etc/barnyard2.conf \  
                         -d /var/log/snort \  
                         -f merged.log \  
                         -w /var/log/snort/barnyard2.waldo \  
                         -a /var/log/barnyard2 \  
                         -u snort -g snort \  

You can now add this snippet to /etc/rc.local run barnyard2 at

Installing BASE

First make sure you have php-adodb installed (available at EPEL). This
installs everything in /usr/share/php/adodb.

yum -y install php-adodb --enablerepo=epel

Then install BASE in your siteroot (assuming default here):

cd /var/www/html/  
wget -O | tar -xvzf -  
ln -s base-1.4.5 base  
cp base/base_conf.php.dist base_conf.php

Then edit the base_conf.php file. Here are my additions/modifications
(other than the Snort MySQL and SMTP info that BASE needs). I used the
same MySQL settings for the “Archive DB” parameters.

$BASE_urlpath = '';  
$DBlib_path = '/usr/share/php/adodb';  
$resolve_IP = 1;

Now navigate to the page and click “Create Base AG”. BAM! Now make sure
that you at least htpasswd the page, since BASE doesn’t have any login



Barnyard2 compilation flags

./configure --with-mysql=/usr/bin/mysql \  
            --with-mysql-includes=/usr/include/ \  

A Note on Waldo Files

To keep track of the most recent logfiles between service restarts,
barnyard uses a “waldo” file. Its contents look like this:

/var/log/snort snort.log 1305050676 0

1305050676 is the most recent timestamp. However, with the setup
above (where I just touch-ed the file), the contents generated by my
command look like this: