Linux IPs & IDs
Linux Intrustion Detection & Prevension
Intrusion Detection & Prevention
What is intrusion Prevention Systems?
Linux Intrusion Prevention or IPS, are tools designed to detect and stop intrusions in their tracks. They come two basic flavors, network-based and host-based. As you may suspect, a network-based IPS is meant to be deployed to monitor the network and a host-based IPS is deployed on a host with the intention of monitoring just a single host.
How these tools work varies from vendor to vendor, but the basics are the same. The network-based tool monitors traffic on the network and matches it to a long list of known signatures. These signatures describe a variety of attacks ranging from simple corrupt packets to more specific attacks such as SQL injection.
Host-based tools tend to have more capabilities as they have access to the entire host. A host-based IPS can look at network traffic as well as monitor files and logs. One of the more popular tools, OSSEC-HIDS, monitors traffic, logs, file integrity, and even has signatures for common rootkits.
More advanced tools have additional detection capabilities such as statistical anomaly detection or stateful protocol inspection. Both of these capabilities use algorithms to detect intrusions. This allows detection of intrusions that don’t yet have signatures created for them.
IPS vs IDS
Unlike it’s predecessor, the Intrusion Detection System, or IDS, when an IPS detects an intrusion it moves to block the traffic and prevent it from getting to its target. As you can imagine, ensuring that the system blocks only bad traffic is of utmost importance. Deploying a tool that blocks legitimate traffic is a quick way to frustrate users and get yourself in trouble. An IDS merely detects the traffic and sends an alert. Given the volume of traffic on a typical network or host today, an IDS is of limited use.
The Redhat Enterprise Packages for Enterprise Linux repository includes two great HIDS apps that every admin should look into. HIDS apps are a bit of a hybrid solution in that they’re both an IDS and an IPS. That is, they can be configured to simply alert when they see issues or they can often be configured to run scripts to react to scenarios that trigger alerts.
Fail2ban is more of an IPS style tool in that it monitors and acts when it detects something awry. One common implementation of fail2ban is monitoring the openssh logs. By building a signature that identifies a failed login, fail2ban can detect multiple attempts to login from a single source address and block that source address. Typically, fail2ban does this by adding rules to the host’s firewall, but in reality, it can run any script you can come up with. So, for instance, you can write a script to block the IP on the local firewall and then transmit that IP to some central system that will distribute the firewall block to other systems. Just be careful, however, as globally blocking yourself from every system on the network can be rather embarrassing.