How To Configure Snort On Debian
Snort is a free network intrusion detection system (IDS). In less official terms, it lets you to monitor your network for suspicious activity in real time. Currently, Snort has packages for Fedora, CentOS, FreeBSD, and Windows-based systems. Exact installation method varies between OSes. In this tutorial, we will be installing directly from the source files for Snort. This guide was written for Debian.
Update, Upgrade, and Reboot
Before we actually get our hands on the Snort sources, we need to make sure that our system is up to date. We can do this by issuing the commands below.
sudo apt-get update sudo apt-get upgrade -y sudo reboot
Once your system has rebooted, we need to install a number of packages to make sure that we can install SBPP. I was able to figure out that a number of the packages that were needed, so the base command is below.
sudo apt-get install flex bison build-essential checkinstall libpcap-dev libnet1-dev libpcre3-dev libnetfilter-queue-dev iptables-dev libdumbnet-dev zlib1g-dev -y
Once all of the packages are installed, you will need to create a temporary directory for your source files - they can be anywhere you'd like. I'll be using
/usr/src/snort_src. To create this folder, you'll need to be logged in as the
root user, or have
sudo permissions -
root just makes it easier.
sudo mkdir /usr/src/snort_src cd /usr/src/snort_src
Installing the Data Acquisition Library (DAQ)
Before we can get the source for Snort, we need to install the DAQ. It's fairly simple to install.
Extract the files from the tarball.
tar xvfz daq-2.0.6.tar.gz
Change into the DAQ directory.
Configure and install the DAQ.
./configure; make; sudo make install
That last line, will execute
./configure first. Then it will execute
make. Lastly, it will execute
make install. We use the shorter syntax here just to save a little bit on typing.
We want to make sure we're in the
/usr/src/snort_src directory again, so be sure to change into that directory with:
Now that we are in the directory for the sources, we will download the
tar.gz file for the source. At the time of this writing, the most recent version of Snort is
The commands to actually install snort are very similar to the ones used for the DAQ, but they have different options.
Extract the Snort source files.
tar xvfz snort-184.108.40.206.tar.gz
Change into the source directory.
Configure and install the sources.
./configure --enable-sourcefire; make; sudo make install
Post-install of Snort
Once we have Snort installed, we need to make sure that our shared libraries are up to date. We can do this using the command:
After we do that, test your Snort installation:
If this command does not work, you will need to create a symlink. You can do this by typing:
sudo ln -s /usr/local/bin/snort /usr/sbin/snort snort --version
The resulting output will resemble the following:
,,_ -*> Snort! <*- o" )~ Version 220.127.116.11 GRE (Build 262) '''' By Martin Roesch & The Snort Team: http://www.snort.org/contact#team Copyright (C) 2014-2015 Cisco and/or its affiliates. All rights reserved. Copyright (C) 1998-2013 Sourcefire, Inc., et al. Using libpcap version 1.6.2 Using PCRE version: 8.35 2014-04-04 Using ZLIB version: 1.2.8
Now that we have snort installed, we don't want it running as
root, so we need to create a
snort user and group. To create a new user and group, we can use these two commands:
sudo groupadd snort sudo useradd snort -r -s /sbin/nologin -c SNORT_IDS -g snort
Since we have installed the program using the source, we need to create the configuration files and the rules for snort.
sudo mkdir /etc/snort sudo mkdir /etc/snort/rules sudo mkdir /etc/snort/preproc_rules sudo touch /etc/snort/rules/white_list.rules /etc/snort/rules/black_list.rules /etc/snort/rules/local.rules
After we create the directories and the rules, we now need to create the log directory.
sudo mkdir /var/log/snort
And lastly, before we can add any rules, we need a place to store the dynamic rules.
sudo mkdir /usr/local/lib/snort_dynamicrules
Once all of the previous files have been created, set the proper permissions on them.
sudo chmod -R 5775 /etc/snort sudo chmod -R 5775 /var/log/snort sudo chmod -R 5775 /usr/local/lib/snort_dynamicrules sudo chown -R snort:snort /etc/snort sudo chown -R snort:snort /var/log/snort sudo chown -R snort:snort /usr/local/lib/snort_dynamicrules
Setting up the config files
To save a bunch of time and to keep from having to copy and paste everything, lets just copy all of the files into the configuration directory.
sudo cp /usr/src/snort_src/snort*/etc/*.conf* /etc/snort sudo cp /usr/src/snort_src/snort*/etc/*.map /etc/snort
Now that the config files are there, you can do one of two things:
- You can enable Barnyard2
- Or you can just leave the config files alone and selectively enable the desired rules.
Either way, you're still going to want to change a few things. Keep reading.
/etc/snort/snort.conf file, you will need to change the variable
HOME_NET. It should be set to your internal network's IP block so it won't log your own network's attempts to log into the server. This may be
192.168.0.0/16. On line 45 of
/etc/snort/snort.conf change the variable
HOME_NET to that value of your network's IP block.
On my network, it looks like this:
ipvar HOME_NET 192.168.0.0/16
Then, you'll have to set the
EXTERNAL_NET variable to:
Which just turns
EXERNAL_NET into whatever your
HOME_NET is not.
Setting the rules
Now that a large majority of the system is set up, we need to configure our rules for this little piggy. Somewhere around line 104 in your
/etc/snort/snort.conf file, you should see a "var" declaration and the variables
BLACK_LIST_PATH. Their values should be set to the paths we used in
var RULE_PATH /etc/snort/rules var SO_RULE_PATH /etc/snort/so_rules var PREPROC_RULE_PATH /etc/snort/preproc_rules var WHITE_LIST_PATH /etc/snort/rules var BLACK_LIST_PATH /etc/snort/rules
Once those values are set, delete or comment out the current rules starting on about line 548.
Now, lets check to make sure that your configuration is correct. You can verify it with
# snort -T -c /etc/snort/snort.conf
You will see output similar to the following (truncated for brevity).
Running in Test mode --== Initializing Snort ==-- Initializing Output Plugins! Initializing Preprocessors! Initializing Plug-ins! ..... Rule application order: activation->dynamic->pass->drop->sdrop->reject->alert->log Verifying Preprocessor Configurations! --== Initialization Complete ==-- ,,_ -*> Snort! <*- o" )~ Version 18.104.22.168 GRE (Build 229) '''' By Martin Roesch & The Snort Team: http://www.snort.org/contact#team Copyright (C) 2014-2015 Cisco and/or its affiliates. All rights reserved. Copyright (C) 1998-2013 Sourcefire, Inc., et al. Using libpcap version 1.7.4 Using PCRE version: 8.35 2014-04-04 Using ZLIB version: 1.2.8 Rules Engine: SF_SNORT_DETECTION_ENGINE Version 2.4 <Build 1> Preprocessor Object: SF_IMAP Version 1.0 <Build 1> Preprocessor Object: SF_FTPTELNET Version 1.2 <Build 13> Preprocessor Object: SF_SIP Version 1.1 <Build 1> Preprocessor Object: SF_REPUTATION Version 1.1 <Build 1> Preprocessor Object: SF_POP Version 1.0 <Build 1> Preprocessor Object: SF_DCERPC2 Version 1.0 <Build 3> Preprocessor Object: SF_SDF Version 1.1 <Build 1> Preprocessor Object: SF_GTP Version 1.1 <Build 1> Preprocessor Object: SF_DNS Version 1.1 <Build 4> Preprocessor Object: SF_SSH Version 1.1 <Build 3> Preprocessor Object: SF_DNP3 Version 1.1 <Build 1> Preprocessor Object: SF_SSLPP Version 1.1 <Build 4> Preprocessor Object: SF_SMTP Version 1.1 <Build 9> Preprocessor Object: SF_MODBUS Version 1.1 <Build 1> Snort successfully validated the configuration! Snort exiting
Now that everything is configured without errors, we are ready to start testing Snort.
The easiest way to test Snort is by enabling the
local.rules. This is a file that contains your custom rules.
If you've noticed in the
snort.conf file, somewhere around line 546, this line exists:
If you don't have it, please add it around 546. You can then use the
local.rules file for testing. As a basic test, I just have Snort keep track of a ping request (ICMP request). You can do that by adding in the following line to your
alert icmp any any -> $HOME_NET any (msg:"ICMP test"; sid:10000001; rev:001;)
Once you have that in your file, save it, and continue reading.
Run the test
The following command will start Snort and print "fast mode" alerts, as the user snort, under the group snort, using the config
/etc/snort/snort.conf, and it will listen on the network interface
eno1. You will need to change
eno1 to whatever network interface your system is listening on.
$ sudo /usr/local/bin/snort -A console -q -u snort -g snort -c /etc/snort/snort.conf -i eno1
Once you have it running, ping that computer. You will start to see output that looks like the following:
01/07−16:03:30.611173 [**] [1:10000001:0] ICMP test [**] [Priority: 0] 192.168.1.105 -> 192.168.1.104 01/07−16:03:31.612174 [**] [1:10000001:0] ICMP test [**] [Priority: 0] 192.168.1.104 -> 192.168.1.105 01/07−16:03:31.612202 [**] [1:10000001:0] ICMP test [**] [Priority: 0] 192.168.1.105 -> 192.168.1.104 ^C*** Caught Int−Signal
You can press Ctrl+C to exit the program, and that's it. Snort is all set up. You may now use any rules that you desire.
Lastly, I want to note that there are some public rules made by the community you can download from the official site under the "Community" tab. Look for "Snort", then just under that there is a community link. Download that, extract it, and look for the