Security Information and Event Management (SIEM) platforms are no longer limited to large enterprises. While proprietary platforms have much to offer small and mid-sized organizations, many security leaders are attracted to the lower licensing costs offered by open source SIEMs. 

These options don't always share the same features as proprietary alternatives, but they can present a compelling opportunity for security leaders with tight budgets. However, implementing an open source SIEM can still be a complex and costly undertaking. By the end of this article, you'll have a clear understanding of open source SIEM tools currently on the market, and whether their capabilities fit your organization's security needs. 

Introduction to SIEM tools

SIEM platforms combine a variety of monitoring and analysis tools into a single, centralized solution. They aggregate log data from your organization's entire tech stack and correlate them to detect threats in real-time, manage investigations into security incidents, and organize incident response workflows. Your SIEM also plays an important role helping your security team communicate risk and prepare compliance audits.  

Since your SIEM gathers data from almost every security and IT tool in the organization, implementing one is a complex and challenging task. Not only must your team successfully integrate the platform with every log-generating asset in your network, but it do so in a way that adheres to regulatory frameworks like PCI-DSS and the European Union's GDPR. 

Benefits and drawbacks of using open source SIEM tools

Security leaders who choose open source SIEM tools often prioritize the following advantages: 

• No licensing fees. Open source tools can be used without paying any licensing fees. This can translate to significant savings for startups and small businesses. 

• Full customizability. Your organization can customize its open source SIEM platform to meet specific security needs. There are no proprietary tools or services attached. 

• Community support. Open source developers often cultivate invested communities, helping users pool resources and gain collective knowledge of the technology. 

• Transparent architecture. Anyone can review, edit, and update open source code. That means open source SIEM tools have transparent software architecture, with no surprises or hidden proprietary features. 

• Reduced vendor lock-in risks. The lack of software licensing costs makes vendor lock-in much rarer among open source solutions. However, it can still happen, depending on how embedded the technology (and specialist expertise required to run it) is in your organization. 

However, compared to proprietary enterprise SIEM solutions, open source tools come with some disadvantages as well: 

• Reduced scalability. Deploying an open source SIEM means integrating the platform on your own IT infrastructure and scaling it to meet your needs as they grow over time. This generally increases the cost as your organization grows. 

• Ongoing engineering and maintenance costs. You may not pay licensing costs, but you will have to hire security engineers capable of maintaining and customizing your open source SIEM. These costs can quickly add up to more than the price of an enterprise SIEM license.  

• Fewer features. Many open source SIEM platforms lack important capabilities like reporting and event correlation. Very few offer advanced features like User Entity and Behavioral Analytics (UEBA), and typically not at a level that competes with enterprise alternatives. 

• Log storage management challenges. Open source SIEMs do not typically include solutions for log storage and management. This issue can lead to unexpected surges in operating costs, creating a need for third-party security log management. 

Top 8 popular open source SIEM tools

1. The ELK Stack (no longer open source)

No list of open source SIEM tools can be complete without mentioning the ELK stack. This is actually a combination of three separate tools — ElasticSearch, Logstash, and Kibana, often in conjunction with Beats, a lightweight log shipper. 

The problem is that the ELK stack is no longer fully open source. Elastic changed its software licensing framework in 2021, separating the ELK stack into two variants: a deprecated free version you can use for legacy compatibility and a professionally maintained enterprise edition. Neither is a complete SIEM system, but the ELK stack can still provide a robust foundation for building SIEM capabilities. 

2. OpenSearch

OpenSearch is a fork of ElasticSearch and Kibana whose development is led by Amazon Web Services. It includes the OpenSearch database and a visualization and analytics tool called OpenSearch Dashboards. 

OpenSearch supports centralized management and comes with a suite of security features like encryption, access control, audit logging, and compliance. It can even support machine learning features through its ML Commons plugin. 

However, OpenSearch does have significant limitations. It does not include core SIEM features like security detections and analytics on its own, and deep customization is not possible due to AWS-imposed limitations. While there is no licensing cost, you still have to host OpenSearch on AWS cloud infrastructure and pay for it according to the AWS pricing model — which can get expensive if not expertly managed. 

3. OSSEC

OSSEC is a hosted security platform that comes in multiple versions, including an open source log-based intrusion detection system. OSSEC+ is also free, but adds machine learning, real-time community threat sharing, and thousands of detection rules. Atomic OSSEC is a paid, enterprise-ready Extended Detection and Response (XDR) platform with its own management console and native integration tools. 

While OSSEC does have SIEM-like capabilities, it is not a full-featured SIEM. In fact, one of the selling points for Atomic OSSEC is native integration with proprietary SIEMs like Splunk, Arcsight, and others. However, the platform can analyze logs from third-party data sources and monitor file integrity, making it a useful technology for security teams that prioritize open source solutions.  

4. SecurityOnion

SecurityOnion is a free Linux distribution that provides intrusion detection and security monitoring tools to IT teams. It expands on the features of existing open source projects like OpenSearch and OSSEC, adding intrusion detection system (IDS) and full packet capture (FPC) capabilities. 

On its own, SecurityOnion provides limited SIEM capabilities. You can enhance it by integrating additional open source tools like Suricata and Zeek, which offer network visibility and traffic analysis. However, some users still prefer to integrate SecurityOnion with the ELK stack for more comprehensive SIEM coverage. 

5. Wazuh

Wazuh is a free platform offering enterprise SIEM and XDR capabilities. It includes built-in active response scripts which allow security teams to build response playbooks for specific threats. It supports custom rules and can integrate with other security platforms to provide extensive coverage. 

One of the biggest advantages Wazuh offers security leaders is its combination of advanced SIEM and XDR features. However, these features can also make the implementation a complex undertaking. You may need additional specialist expertise to ensure best-in-class results. 

6. OSSIM

AT&T Open Source Security Information Management (OSSIM) is the open source version of AlienVault's USM Anywhere SIEM platform. It allows security teams to gather and analyze security event data from many different sources and helps them conduct vulnerability management and behavioral monitoring tasks. 

OSSIM has a more limited feature set than USM Anywhere, which can make it less effective in certain environments. For example, OSSIM can only deploy on a single server and does not protect cloud services. Manual plugin management can be a time-consuming task, which USM Anywhere streamlines considerably.   

7. Prelude

Prelude is a SIEM framework that combines multiple other tools into a single interface. Similar to other open source platforms on this list, Prelude comes both as a free open source platform with limited functionality and a paid enterprise-ready option. 

Prelude's open source option has significant limitations that make it unfeasible for an active commercial organization. The company itself offers the open source edition with a disclaimer saying that it is designed for "evaluation, research, and test purposes in very small environments", with significantly lower performance than the paid version of the same product. 

8. Apache Metron

Apache Metron combines a variety of technologies into a unified secuirty monitoring and analysis tool. It is primarily an extension of Cisco's OpenSOC platform, but with enhanced SIEM-like capabilities. Like many other entrants on this list, it is not a full-fledged SIEM but a security framework that combines multiple open source projects into a single platform. 

Metron's architecture relies on other Apache projects to function. If your IT team is already familiar with Apache solutions like Hadoop, Nifi, and Kafka, implementing Metron will be much easier. It is an extensible plugin-centric framework that supports a wide range of tools and services, but on a limited number of operating systems and environments. 

Is an open source SIEM the right option for your organization?

Many organizations pursue open source SIEM implementations to meet regulatory compliance standards and gain security alert visibility through a centralized platform. The ability to avoid license costs makes the open source option especially attractive. However, this choice often comes at the cost of key features and essential capabilities. 

Commercial tools may come with licensing fees, but they often reduce the overall number of hours security professionals must work to produce meaningful results. Instead of deploying a new SIEM in-house, consider augmenting your security tech stack with next-generation SIEM capabilities managed by professional third-party security analysts. Managed detection and response vendors like Lumifi can help you achieve your security and compliance goals at a fraction of the cost of hiring an in-house security analyst team.