Snort is by far the most popular open-source network intrusion detection and prevention system (IDS/IPS) for Linux. Snort can conduct detailed traffic analysis, including protocol analysis, packet content searching and matching, all in real-time. The latest Snort rule sets are available for download either for free or with a paid subscription.
You can install Snort from its source code or binary rpm/deb packages on Linux. There are several reasons why you want to build Snort from source code, not install it from Linux packages. For example, you want to use the latest version of Snort, which may not be available in Linux distro repositories. Also, you may want to customize Snort binary in any way (e.g., plug in a custom DAQ module, use a particular version of libpcap library, etc.).
In this tutorial, I will describe how to compile and install Snort from source code.
Compile and Install Snort and Its Dependencies
First, install prerequisites for compiling Snort.
Next, build and install libdnet from its source code. The "-fPIC" C flag is necessary if you compile it on 64-bit platform.
$ tar xvfvz libdnet-1.12.tgz
$ cd libdnet-1.12
$ ./configure "CFLAGS=-fPIC"
$ sudo checkinstall
The checkinstall command above will build .deb package. and while doing so, ask you several questions. You can accept default values.
Install .deb package, and create a symbolic link where Snort looks for libdnet.
$ sudo ln -s /usr/local/lib/libdnet.1.0.1 /usr/lib/libdnet.1
Next, build and install DAQ (Data Acquisition) library. DAQ is an abstraction layer for packet I/O, which allows you to plug different DAQ modules into Snort, to support different hardware/software interfaces for packet I/O, without changing Snort itself. DAQ source code is available from here.
$ cd daq-2.0.0
$ sudo checkinstall
$ sudo dpkg -i daq_2.0.0-1_amd64.deb
Next, compile and install Snort itself. Snort source code is available here.
$ cd snort-2.9.5
$ sudo checkinstall
$ sudo dpkg -i snort_2.9.5-1_amd64.deb
$ sudo ln -s /usr/local/bin/snort /usr/sbin/snort
Finally, run ldconfig command, so that dynamic linker run-time bindings for libdnet and DAQ libraries are properly set up.
After this, verify that Snort is installed successfully.
,,_ -*> Snort! <*- o" )~ Version 2.9.5 GRE (Build 103) '''' By Martin Roesch & The Snort Team: http://www.snort.org/snort/snort-team Copyright (C) 1998-2013 Sourcefire, Inc., et al. Using libpcap version 1.3.0 Using PCRE version: 8.31 2012-07-06 Using ZLIB version: 1.2.7
Configure Snort and Download Snort Rule Sets
After installation, go ahead and configure Snort as follows.
For security reason, it is recommended to create a separate Linux user which Snort will run as.
$ sudo useradd snort -d /var/log/snort -s /sbin/nologin -c SNORT_IDS -g snort
Create a log directory for Snort.
$ sudo chown snort:snort /var/log/snort
Download Snort rule sets. You can download a registered user release for free. After download, install and configure Snort rules as follows.
$ sudo tar xvfvz snortrules-snapshot-2950.tar.gz -C /etc/snort
$ sudo touch /etc/snort/rules/white_list.rules /etc/snort/rules/black_list.rules
$ sudo mkdir /usr/local/lib/snort_dynamicrules
$ sudo chown -R snort:snort /etc/snort/*
$ sudo mv /etc/snort/etc/* /etc/snort
Edit a default Snort configuration to point to correct ruleset directories. Also define HOME_NET which is the network to protect with Snort.
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 ipvar HOME_NET 192.168.1.0/24 ipvar EXTERNAL_NET !$HOME_NET
Run Snort in Self-Test Mode
After configuration is done, you can test Snort by using the following command. This command will launch Snort in self-test mode, and check if rules are successfully loaded. I assume that eth0 is the network interface that Snort is listening on.
Upon launch, you will see that Snort loads a set of Snort rules, and starts validating the configuration.
If Snort passes all the tests successfully, you should see the following messages:
Snort successfully validated the configuration! Snort exiting
To conclude, I show in this tutorial how to install and configure Snort IDS in the Ubuntu environment. Note that Snort is a single-threaded application. If your Linux server has multi-core CPUs, you need to spawn multiple Snort processes to leverage those cores. Alternatively, you can consider multi-threaded IDS such as Suricata.
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