SIEM tools are fast turning into a must-have for security-focused businesses worldwide. With their proven abilities in threat protection, detection, and mitigation, SIEM systems are beneficial in safeguarding businesses from unwanted threats. Our last post explained what SIEM is, the value it adds, how SIEM works, and what to look for in a SIEM solution. As with most IT solutions and services, SIEM too has plenty of proprietary and open-source options to choose from. In this article, we’ll take a look at some of the best open-source SIEM tools for businesses of all sizes.

Is open-source SIEM worth it?

We all know that, when implemented correctly, SIEM is a powerful weapon in any IT security arsenal. While considering implementing SIEM at your organization, one of the significant obstacles you may come across is cost. Proprietary SIEM tools are expensive – their entry-level plans may not have all the features you need, deployment costs could be high, and some of them might also require specialist skill and training for your teams. If budgets or high entry costs stop you from implementing SIEM for your business, try using open-source projects.

There are plenty of open-source SIEM tools available today. You could obtain them for free, reduce your acquisition cost, and reduce deployment and implementation costs to a bare minimum. While open-source SIEM tools may not be an all-in-one solution, you can still expect some solid functionality. Some of the best open-source SIEM projects have the backing of a large community of security experts who leverage their experience and knowledge to continuously iterate and improve these projects. While you may have to use these tools in combination with other tools that support better reporting, visualization, or event correlation, the right open-source tool can be a great (and significantly cheaper) stepping stone to better security for your business.

With that said, let’s look at a list of the best open-source SIEM tools that are worth exploring. While we’ve numbered this list, it does not indicate an order of best to least preferred. 


OSSIM is one of the most popular open-source SIEM systems that combines other open-source tools that aid security, threat detection, and prevention. It includes key SIEM components such as event collection, processing, and event correlation. Some of OSSIM’s components include Nagios Core for monitoring and alerting, Snort for network intrusion detection and prevention, Munin for traffic analysis and service watchdogging, OpenVAS for vulnerability assessment and management.

The OSSIM project is the basis for AlienVault, which AT&T Cybersecurity later acquired. 

2. Sigma

Sigma is an open signature format that allows you to define log events. You can apply Sigma rules to any log file format to augment its data with relevant security information. As the Sigma project states, “Sigma is for log files what Snort is for network traffic and YARA is for files.” 

You can use Sigma with any log forwarder, aggregator, or data flow manager to augment log data with security information right within the event stream. Apica ships with built-in Sigma rules that help you automatically enhance log data from multiple sources with security-related events that were detected. 

3. The ELK Stack

Also known as Elastic Stack, the ELK Stack consists of various open-source SIEM tools like Elasticsearch, Logstash, and Kibana. Through embedded Logstash components, ELK can aggregate logs from almost all data sources. It uses Elasticsearch for storing and indexing time series data and Kibana to visualize log data.

The ELK stack can be a great building block for your SIEM system. However, the recent shift of Logstash and Kibana to SSPL licenses makes two of its core components technically not open-source. Consequentially, this switch in licensing embeds contributions made by the public and you in proprietary products. The other disadvantages of the ELK stack include a lack of built-in security rules, reporting, or alerting capabilities. The ELK stack is also famous for being resource and operations-heavy, meaning that you might end up spending a lot of time and money in building and managing the perfect ELK stack implementation for your company. 

4. Prelude OSS

Prelude OSS is the open-source version of Prelude SIEM and is a universal SIEM system that helps normalize log data. It is truly agentless and therefore collects, standardizes, correlates, and reports all security-related events occurring within an IT environment. It normalizes security events into the standard IDMEF format, works with various log types, and can be used to standardize your log data before feeding them into other security tools in your arsenal. 

Being the open-source variant of a proprietary system, Prelude OSS is great for smaller environments and may not perform as well as its proprietary version. You can consider using Prelude OSS as an evaluation or test version of Prelude SIEM. 


Open Source HIDS Security (OSSEC) is an open-source host-based intrusion detection system that performs log analysis, threat detection, registry monitoring, alerting, and active response. It works with most operating systems, including Windows, Linux, Solaris, macOS, OpenBSD, and FreeBSD. It supports extensive customization through configuration options, the addition of custom alert rules, and custom scripts to perform reactive actions against threats. 

OSSEC also has an impressive log analysis engine that you can leverage to correlate and analyze logs from multiple devices. 

6. Snort

Snort is an open-source intrusion detection and prevention system that you can use for real-time network traffic analysis and packet logging on IP networks. You can also use Snort to detect attacks or possible probes. You can configure Snort to work in three main modes:

  • Sniffer mode, where Snort analyzes network packets and displays them on the console
  • Packet logger mode, where Snort logs packets to the disk
  • Network Intrusion Detection System mode, where Snort leverages a set of rules that define threat activity to analyze network traffic to find packets of data that match against them and trigger alerts for users.

7. MozDef

The Mozilla Defense Platform (MozDef) is an open-source SIEM layer developed by the Mozilla Corporation that sits atop Elasticsearch. It enables security teams to collect, store, and manage events and logs from various systems, makes log and event data searchable, and creates alerts against specific events in the log stream. MozDef also integrates easily with tools like AWS CloudTrail and GuardDuty. Some of MozDef’s key components include NGINX, RabbitMQ, MongoDB, and Elasticsearch.

8. Wazuh

Wazuh is an open-source SIEM system born from the OSSEC project that you can use for threat detection, prevention, and response. You can also use Wazuh to comply with industry standards and regulations such as PCI DSS, GPG 13, and GDPR. Wazuh ships with an integration with Kibana that makes for an excellent UI for data visualization and analytics. It also ships with an agent that you can install on any endpoint across various operating systems. The Wazuh server helps you manage Wazuh agents and analyzes data received from these agents, processes it, and identifies threats within that data. 

Having evolved from OSSEC, Wazuh is a more mature SIEM solution that provides everything a SIEM practitioner needs.


There are several fantastic open-source SIEM systems available today that offer great functionality and ease of use. However, not all of them are genuinely complete. A well-rounded SIEM system should:

  • Collect and unify all of your IT data
  • Manage and store data for longer durations
  • Allow you to monitor and analyze your machine data constantly; and, 
  • Allow for data visualization, event correlation, and alert generation. 

Without these capabilities, you’d still be on the lookout for yet another accessory to your SIEM system. Most of the SIEM systems listed above use the ELK stack in some form or the other as their base layer. The ELK stack is famous for being difficult to install, integrate, manage, and optimize. Moreover, the ELK stack requires constant updates and upgrades and is prone to vulnerabilities, just like any other open-source system. 

This is why many consider spending the extra money to go for a full-fledged, enterprise-grade proprietary SIEM software with proven automation, log management, and visualization capabilities. While open-source solutions offer a financial benefit, it seems more reliable to consider a proprietary tool that offers more comprehensive protection and is easier to use.

Try the SIEM-ready Apica data platform

One such tool worth considering is the Apica data platform. Apica helps you:

  • Unify all of your machine data from disparate sources on a single platform
  • Augment your log data with security events using built-in Sigma rules
  • Meet PCI DSS and SOC 2 compliance requirements through powerful constructs to secure and manage data
  • Scale seamlessly to cope with periods of high data ingestion and usage
  • Automate SecOps by triggering and sending alerts and kicking off threat remediation and security workflows
  • Have full-indexed and searchable data stored in S3 for as long you wish, without any storage tax. 

With SaaS and PaaS plans starting as low as $0.33 per GB per month, Apica can meet any budget. If you’d like to try out Apica, sign up for a 14-day free trial of Apica SaaS, or deploy the free-forever Apica PaaS Community Edition