What is Open-Source Intrusion Detection?

While you might be familiar with Suricata due to its popularity in the world of network security, you might not be familiar with why open-source intrusion detection tools like Suricata are so widely used. In this blog post, we will define open-source intrusion detection, discuss what makes up a network-based intrusion detection system, and provide examples of different IDS options.

What is open-source intrusion detection?

An open-source intrusion detection system (IDS) is a security software system that monitors an organization’s network for malicious activity and that is freely available for anyone to use, modify, and distribute. Instead of relying on pre-built commercial security software, open-source intrusion detection systems offer a different approach based on transparency, flexibility, customizability, and community collaboration.

The core idea is that the IDS’s code is open for anyone to download, use, alter, and improve. This openness allows for a wide range of individuals to contribute to its development while also tailoring the system for their own unique needs. The rules used by the IDS are also commonly shared in various threat intelligence sharing platforms, such as MISP, enabling users to support each other and stay up to date with new and emerging threats.

Open-source intrusion detection systems are an incredibly cost-effective option for many organizations because they eliminate the licensing costs associated with commercial security software, making it an attractive option for personal use or budget-conscious organizations.

What is a network-based intrusion detection system?

A network intrusion detection system is any IDS that primarily functions on the network rather than on an individual host. Three main benefits come from network-based intrusion detection:

• Network Traffic Visibility: A network intrusion detection system sits at a strategic point on your network, typically deployed on a network tap or mirrored port. This allows it to capture and analyze all traffic flowing through that point, providing a comprehensive view of network activity.
• Threat Detection Capabilities: By analyzing network traffic patterns and comparing them against threat signatures, a network intrusion detection system can identify malicious activity like malware downloads, intrusions, and network attacks.
• Scalability and Efficiency: Some network intrusion detection systems are designed to handle large volumes of network traffic efficiently. This makes it suitable for protecting even the most high-volume networks.

It is important to note that some network-based IDS tools can technically be configured into a limited host-based IDS in some scenarios. However, this is not its typical or recommended use for several reasons:

• Limited Visibility: When deployed on a single host, IDS can only monitor traffic to and from that specific device, offering a much narrower view of potential threats compared to network-wide monitoring.
• Resource Consumption: Running an IDS on individual devices can consume significant system resources, potentially impacting device performance. This might not be ideal for resource-constrained systems.
• Security Focus: Network-based IDS offers a more strategic approach to security. By monitoring the entire network, you can identify threats targeting any device on your network, not just the host running the IDS.

What is an example of a free open-source IDS?

The best free open-source IPS/IDS is Suricata.

Suricata is a powerful network security tool that monitors your network for malicious activity and is freely available under the GNU General Public License (GPLv2). This means anyone can use, modify, and distribute Suricata without any licensing fees.

Suricata is by far the best open-source IDS, known for its efficiency and ability to handle large volumes of network traffic without compromising performance. It uses deep packet inspection to detect more sophisticated threats that might try to hide malicious payloads within seemingly normal data packets. Suricata can be configured as an IDS for passive monitoring or as an IPS for active blocking of unwanted traffic.

Suricata benefits from a large and active community that develops and maintains a vast library of rules to identify various threats. These rules are regularly updated and commonly shared on platforms like the Malware Information Sharing Project (MISP). There is even an annual conference for Suricata users called Suricon, which historically provides workshops and lectures on Suricata topics, development, and best practices.

Two other popular options are Snort and Zeek, though they are not as effective, efficient, or flexible as Suricata.

Which is better, Suricata or Snort?

When comparing Suricata to the Snort IDS, both stand out as impressive open-source intrusion detection tools. However, Suricata offers some distinct advantages that Snort does not possess:

• Native Multi-Threaded: Suricata utilizes a multi-threaded architecture, allowing it to handle high-traffic environments more efficiently than Snort's single-threaded approach. This translates to better performance on modern hardware.
• Network Security Monitoring (NSM) data: Unlike Snort, Suricata can generate rich NSM data in formats like JSON (EVE). This data provides valuable insights into overall network activity, making it easier to identify trends and potential anomalies beyond just malicious traffic.
• Conditional PCAP storage: Suricata allows for conditional PCAP (packet capture) storage. This means you can configure it to only capture packets that meet specific criteria, saving valuable storage space compared to Snort, which captures all packets by default.

Other factors to consider:

• Rule compatibility: Suricata can leverage most Snort rules with some adjustments, making the transition easier. It also has its own growing rule set.
• Resource consumption: While Suricata is generally more efficient, it still requires more resources than Snort, especially on low-powered devices.
• Community and support: Both Snort and Suricata have active communities, but Snort has been around longer and might have a wider range of readily available resources.

Ultimately, the best choice depends on your specific needs and network environment. Both Snort and Suricata offer significant value for network security, and trying both could help make an informed decision.

Learn More About Suricata

To begin learning more about Suricata and open-source intrusion detection tools, we recommend downloading the open-source book published by Stamus Networks titled “The Security Analyst’s Guide to Suricata” — the first practical guide to threat detection and hunting using Suricata, the world’s most popular open-source network security engine.

Written for security operations center (SOC) analysts and threat hunters who use Suricata to gain insights into what is taking place on their networks, the book provides vital information on entry points and an in-depth analysis of the most important Suricata features.

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