As it turns out, before you can play with OSSEC and begin learning the intricacies of host-based intrusion detection, you need to install the software. Installation itself is pretty easy and fairly straightforward, provided you know how you want to install and run the system.
What do I mean by this? Well, there are three ways to install the OSSEC software. It can be installed as standalone, as a server, or as an agent. These are pretty much what they sound like. A standalone installation is generally used when you’re administering a single machine, or when circumstances prevent you from running a centralized server. A server/agent installation is for larger installations with centralized management.
For both installation types you need to start with the raw source. From there you can run the install script and choose the type of installation you want. Alternatively, if you’re installing on a linux distribution that uses RPM for package management, you can grab a copy of the source RPM for the latest version here. The RPM version only supports the server/agent type, though you can probably run the server as a standalone install. Note: I make no guarantees about the RPMs I provide, you are expected to know what you are installing and take appropriate precautions such as verifying what you have downloaded.
If you’re going with the raw source, grab a copy here. The current release as of this writing is version 2.5. Download the source, unpack it, and run the installation script. The installation script must be run as root. You probably want to check the md5 and/or sha1 sum prior to installation, just to make sure that the code is original.
# wget http://www.ossec.net/files/ossec-hids-2.5.tar.gz
# sha1sum ossec-hids-2.5.tar.gz
# tar zxvf ossec-hids-2.5.tar.gz
# cd ossec-hids-2.5
Just follow the prompts an the installer will take care of the rest, including compiling the software.
The RPM install is simplified a bit as you only have to compile the code once per server architecture you want to support. In other words, if you have both 32-bit and 64-bit installations, you’ll likely want to compile the software twice. Once compiled, you have three packages, ossec-hids, ossec-hids-server, and ossec-hids-client (client = agent). The ossec-hids package is installed on every system while the server and client packages go on the appropriate systems.
In order for the agents to talk to the server, you must have port 1514 open. Additionally, you need to register the agents with the server. This is a pretty simple process, though it has to be repeated for every agent. Detailed instructions can be found here. The short and simple version is as follows:
1) Run /var/ossec/bin/manage_agents and choose to add a new agent. Follow the prompts and enter the appropriate data.
2) While still in manage_agents, select the option to extract the agent authentication key. Copy this key as you need to paste it into the agent.
3) On the agent, run /var/ossec/bin/manage_agents. Choose to import the server key. Paste in the key you copied previously.
And that’s all there is to adding a new agent. There are ways to script this, but they are a bit out of scope for an introduction article. If you’re interested in scripting this process, please check the OSSEC mailing list for more details.
Finally, after installation comes configuration! Tune in tomorrow for more details!