Top 5 Free Open Source SIEM Tools [Updated 2025]

Security information and event management systems are now used by medium-sized and even small organizations. Open Source SIEMs are compelling for new adopters because of their low licensing cost and growing feature set. Which open source SIEMs are out there, and how do they compare to the traditional enterprise offerings?

SIEM security systems used to be for large organizations only, but they are increasingly adopted by medium-size and even small organizations. Open Source SIEMs are compelling for new adopters because of their low licensing cost and growing feature set. Which open source SIEMs are out there, and how do they compare to the traditional enterprise offerings?

What is SIEM?

SIEM (security information and event management) is a security and auditing system. It is not a single tool, but rather a ‘toolbox’ of multiple monitoring and analysis components.

SIEMs aggregate data from hundreds of security and IT tools across the organization, uses statistical correlations and rules to convert events and log entries, and turn them into usable information. Security teams use this information to detect threats in real time, manage forensic investigations on security incidents, organize incident response, and prepare compliance audits.

SIEM is now a standard security approach. An increasing number of organizations are adopting SIEM due to the ongoing increase in cyber attacks and stricter security regulations. Changes to regulations like PCI DSS and the European Union’s GDPR have made it imperative that system and application log events are removed from individual servers and stored securely for investigation and action.

Open Source SIEM vs. Enterprise-grade SIEM

Security information and event management is a foundational system in modern cybersecurity. Other security tools represent information flows, which the SIEM can process and extract value from. Not all SIEMs have the same capabilities; choosing a SIEM that suits the needs of your organization can mean the difference between preventing and missing a catastrophic security breach.

Open source SIEM

Organizations can use open source SIEM tools to reduce software licensing costs and evaluate certain capabilities before extending their product investments. Open source SIEM solutions provide basic capabilities that can suit the needs of smaller organizations that are starting to log and analyze their security event information.

Limitations of open source SIEM

• As an organization grows, open source SIEM software can become labor-intensive.
• An organization may save money on licensing costs, but spend money on continual maintenance.
• Many open source SIEM solutions lack key SIEM capabilities, such as reporting, event correlation, and remote management of log collectors.
• An organization may have to combine open source SIEM with other tools.
• Open source SIEM typically requires a high level of expertise and time to deploy effectively.
• Open source SIEMs typically do not provide or manage storage, a sensitive issue because of the massive volumes of data.

Enterprise-grade SIEM

Enterprise SIEM solutions offer improved management of configuration and installation, correlation configurations, filters, and pre-built visualizations for the most prevalent use cases. They enable organizations to monitor large scale data center activities and centrally manage and configure security-relevant applications.

Perhaps most importantly, currently only enterprise SIEM platforms provide the capabilities of next-generation SIEM. Next-gen enterprise SIEMs come with two new technologies that can save time for security teams and dramatically improve incident detection and response:

• User and entity behavior analytics (UEBA) – goes beyond rules and correlations, leveraging AI and machine learning to look at behavioral patterns of users and IT systems and find high-risk anomalies that may indicate threats.
• Security orchestration, automation and response (SOAR) – integrates with enterprise systems and orchestrates them to automate incident response processes, such as mitigating a malware or data exfiltration attack.

Top Open Source SIEM Tools

Tips from the expert

Steve Moore is Vice President and Chief Security Strategist at Exabeam, helping drive solutions for threat detection and advising customers on security programs and breach response. He is the host of the “The New CISO Podcast,” a Forbes Tech Council member, and Co-founder of TEN18 at Exabeam.

In my experience, here are tips to help organizations effectively evaluate and deploy open-source SIEM solutions while understanding when to transition to enterprise-grade systems:

Combine open-source SIEM with complementary tools
Enhance open-source SIEM functionality by integrating it with standalone tools for intrusion detection (e.g., Suricata) or behavioral analytics (e.g., open-source UEBA frameworks). This provides a modular approach to building advanced capabilities.

Start small and test with open-source SIEM in low-risk environments
Deploy open-source SIEM tools like ELK or OSSIM in a non-critical environment first. This allows your team to familiarize themselves with the setup, customization, and performance without risking vital business systems.

Leverage community-driven plugins to extend functionality
Open-source tools often have a rich ecosystem of community-built plugins. For example, extend ELK’s capabilities by integrating security-focused plugins for alerting or anomaly detection. This bridges some of the gaps between open-source and enterprise-grade tools.

Implement strict logging and storage policies early
Open-source SIEMs like Apache Metron can generate large data volumes. Establish clear data retention policies and optimize storage formats to avoid performance bottlenecks and unmanageable costs.

Use managed versions of open-source SIEM for hybrid benefits
Managed offerings like SIEMonster’s premium version combine open-source cost savings with enterprise-grade features, such as user behavioral analytics and threat intelligence, while reducing deployment complexity.

Open Source Benefits vs. Costs

Open source SIEMs have matured considerably over the past decades and are deployed successfully in many organizations. However, while the main driver for adoption is reduced license costs, it is well known that license costs are only a fraction of the total cost of ownership of SIEM systems. Additional and possibly larger components include:

• Hardware and storage, especially for medium-to-large enterprises, present a huge cost and management complexity
• Analyst time is the most precious resource in most security teams, and analysts are a must to make any use of SIEM alerts

Exabeam is a next-generation SIEM platform built as an enterprise-grade platform on top of ElasticSearch, which addresses these two pain points and cost centers:

• Provides unlimited cloud-based storage at a fixed cost
• Uses next-gen SIEM capabilities like UEBA and SOAR to dramatically reduce analyst time