By Eleanor Bennett


9 min read

Security Information and Event Management (SIEM) is a combination of Security Information Management (SIM) and Security Event Management (SEM). A SIEM solution provides real-time analysis of security alerts generated by applications and networks. SIM is the collection, monitoring and analysis of security-related data such as log files into a central repository for trend analysis.

SEM is the process of network event management including real-time threat analysis, visualization and incident response. It operates by using data inspection tools to centralize the storage and interpretation of logs or events that are generated by other software running on a network. SIEM tools are important in the identification of cyber attacks and offer real-time analysis of security alerts.

Log files are great with threat detection and any comprehensive SIEM tool will have log management capabilities as one of its features. Free and Open-source SIEM tools have recently grown in their popularity. While they are limited in their capabilities (compared with their paid counterparts), they have found much usage among small to medium size organizations. In this post, we’ll look at some of the best free and open source SIEM tools out there today.

1. AlienVault OSSIM

Alienvault OSSIM was developed by AlienVault as a single unified platform equipped with some of the most valuable security capabilities including:

  • Asset discovery
  • Intrusion detection
  • SIEM Event Correlation
  • Vulnerability assessment
  • Behavioural monitoring

OSSIM carries out event collection, normalization and correlation making it a comprehensive tool when it comes to threat detection. It has short-term logging and monitoring capabilities, long-term threat assessment and built-in automated responses. Some of the Pros and Cons of this tool include;


  • Can be operated on-premise and virtually
  • Requires only a single server
  • There is community support via its product forum
  • Developers provide ongoing development increasing its value to users


  • Limited flexibility making its customization a long process.
  • Labour-intensive setup.

2. SIEM Monster

siemmonster  SIEM Monster is a favourite for many organizations because of the possibility to customize it according to organisational needs of any size whether it be a small, medium or large enterprise. It brings together several open source solutions into one centralized platform and provides threat intelligence in real-time, protecting its users against real-time attacks.

Some of SIEM Monster’s features include;

  • Human-Based Behavior- It is equipped with correlation options ensuring that the threats recorded are true and that false positives are minimized.
  • Threat Intelligence- Real-time threat intelligence with commercial or open-source feeds to stop real-time attacks.
  • Deep Learning- Machine Learning is at the back of this feature and it teaches the program to automatically kill any attacks that might arise.

A key positive for this tool is that it can be run on-site or in the cloud.

3. Wazuh

wazuh  Wazuh is a common choice among enterprises because it is fully equipped with capabilities in threat detection, integrity monitoring, incident response and compliance. Wazuh collects, aggregates, indexes and analyzes security data making it possible for organizations to detect intrusions, identify threats and any behavioural anomalies that may arise. It boasts many features including;

  • Intrusion Detection
  • Log Data Analysis
  • File Integrity Monitoring
  • Vulnerability Detection
  • Configuration Assessment
  • Incident Response
  • Regulatory compliance
  • Cloud security
  • Containers security

Wazuh is a great enterprise choice because it’s flexible, scalable, free of vendor lock-in and has no licence costs. Its downside has been a limitation in its power to handle numerous alerts which sort of compromises its integrity.

4. Snort

snort  Snort is an open-source Intrusion Prevention System (IPS). It is a great tool for enterprises seeking a tool that can do network traffic analysis in real-time.

It is also equipped with log analysis capabilities and the ability to display traffic or dump streams of packets to log files. Users have access to a user manual, FAQ file and guides on how to locate and use Oinkcode. Snort has three great uses:

  • As a packet sniffer like tcpdump
  • As a packet logger which is most useful for network traffic debugging
  • As a comprehensive network intrusion prevention system
  • Snort is a bit technical in nature with a not very user-friendly interface.


ossec  Is a scalable, multi-platform, open-source, host-based Intrusion Detection System. It is popular because it runs on most operating systems including Linux, OpenBSD, FreeBSD, MacOS, Solaris and Windows.

OSSEC brags a powerful correlation and analysis engine with features including;

  • Log analysis
  • File integrity monitoring
  • Windows registry monitoring
  • Centralized policy enforcement
  • Rootkit detection
  • Real-time alerting and active response.
  • Compliance Auditing
  • System Inventory

Security professionals working in big enterprises have a liking for this tool because it allows you to monitor many networks from a single station. You can also count on the inclusive community of OSSEC developers and users simplifying your time using this tool.

Among other pros, OSSEC can operate in both server-agent mode and serverless modes making it very flexible.

6. Sagan

sagan Sagan was developed by Quadrant Information Security as a high-performance open-source tool operating real-time analysis and correlation. It operates under Linux, FreeBSD and OpenBSD operating systems.

Sagan’s key features which also double as benefits include;

  • Compatibility with popular graphical-base security consoles like Snorby, BASE, Squil and Evebox.
  • Its CPU and memory resources are lightweight making it easy to set up and maintain.
  • It allows data exportation from other SIEM tools using Syslog.
  • It can track the geographic component of any events that happen so you can attack a location to every event.
  • It can also monitor the time that events take place.

A user can set certain criteria on how the tool makes alerts which protect the user from being bombarded with alerts.


logit provides a highly affordable SIEM tool that is built on hosted ELK. The ELK Stack is composed of several complimentary SIEM offerings including ElasticSearch, Logstash, Kibana and Beats. ELK also plays a key part of the architecture behind OSSEC, Apache Metron, SIEM Monster and Wazuh, which are all mentioned in this blog.

SIEM as a Service is’s managed offering providing all of the key components required for organisations to secure their operations at one of the most affordable rates in the industry.

With high availability and SLAs up to 99.999%, you can be assured that provides an ideal solution for scalable Security Information and Event Management.

Features include:

  • Advanced role-based access controls
  • Lightning-fast deployment
  • Hundreds of integrations
  • Compliance & auditing
  • Affordable SIEM
  • Event correlation
  • Scheduled reports
  • Alerting & notifications

8. Apache Metron

apachmetron  Apache Metron is the perfect tool for organizations looking for Big Data Security. It provides a scalable advanced security analytics framework providing organizations with the ability to detect cyber anomalies and equipping those organizations to be able to rapidly respond to the anomalies that arise.

Apache Metron has many great features including;

  • SOC Analyst identifying the alerts that come up
  • SOC Investigator to identify and triage anomalies
  • SOC Manager to automatically create cases with integrated workflow systems
  • Forensic Investigator undertaking evidence collection response in real-time
  • Security Platform Engineer- a single platform that manages and operates the integration and processing of cyber data.
  • Security Data Scientist to perform data science lifecycle activities, train, evaluate and score analytical models.

9. Prelude

prelude  Prelude is a universal SIEM system and it collects, normalizes, sorts, aggregates, correlates and reports all security-related events independent of the product brand or licence giving rise to such events. Third-party agents to this tool include Auditd, OSSEC, Suricata, Kismet and ClamAV.

The key features of Prelude include:

  • Pilot- Prelude offers a central point of control for your information system’s security. It collects all the traces, correlates and aggregates them to provide an easily operated overall view.
  • Detect- It detects any hacking attempt in the security system by combining various detection technologies.
  • React- It handles any intrusion of the security of the system and provides support throughout the mediation phase of attacks by carrying out investigation and resolution of workflow functionalities.

10. Splunk Free

splunk  Splunk Free as the name suggests is the free version of Splunk Enterprise, its paid version. Splunk Enterprise is a comprehensive SIEM tool and its free version shares a number of its features but may not handle all the security needs of your organization especially as it grows.

Splunk Free allows you to index up to 500MB of data every day and you have lifetime access (no expiration date).

This means you can add 500 MB of fresh data daily and as your data size needs to expand, you can turn to the enterprise version. To say briefly, Splunk features Artificial Intelligence and Machine Learning which make it become more versatile and more intelligently addresses threats as the days go by.

Splunk Free has some features disabled including;

  • Alerting/monitoring
  • No user roles so no login capabilities
  • Deployment management capabilities
  • Index clustering

Therefore as you consider using this tool, you will be limited in the above ways. Nonetheless, it is one of the tools smaller enterprises have found value using.

11. Mozdef

mozdef  Mozdef was developed by Mozilla and is operated in an AWS account. It is one of the large arsenal of tools available for attackers helping them coordinate, share intelligence and fine-tune attacks in real-time.

The goals behind the development of Mozdef include;

  • Providing a platform for defenders to rapidly discover and respond to security incidents.
  • Providing the necessary metrics for security events and incidents.
  • Facilitating repeatable, predictable processes for incident handling.
  • Driving collaboration in real-time amongst incident handling.

12. Security Onion

securityonion Security Onion is a Linux distribution designed for intrusion detection and Enterprise Security Monitoring (ESM). It was developed in 2008 by Doug Burks who later launched Security Onion Solutions in 2014.

It is a flexible tool providing both host-based and network-based intrusion detection systems (IDS), as well as Full Packet Capture (FPC). If your organization is searching for a tool that will make threat hunting, enterprise security monitoring and log management seamless, then this one is a viable option.

Security Union is a collection of Elasticsearch, Logstash, Kibana, Suricata, Zeek (formerly known as Bro), Wazuh and many other security tools.

It can be used in several capacities including;

  • NIDS- It collects network events from Zeek, Suricata and other tools to complete coverage of your organization network.
  • HIDS- It supports host-based event collection agents including Wazuh, Beats and Osquery.
  • Static Analysis (PCAP Import)- It can be used to import PCAP files for quick static analysis and case studies.

It mainly operates with the following data types; Agent, Alert, Asset, Extracted Content, Full Content, Session and Transaction.

13. Suricata

suricata Initially built as an Intrusion Detection and Prevention tool (IDS/IPS) and has now grown, adding important protocol detection and Network Security Monitoring (NSM) capabilities.

Some of its great features include;

  • NSM: Suricata can log HTTP request logs and store TLS certificates, extract files from flows and store them on a disk.
  • Automatic Protocol Detection for protocols such as HTTP on any port and applying the proper detection.

A great pro of this tool is its high-performance capabilities whereby a single Suricata instance is capable of inspecting multi-gigabit traffic.

14. Graylog

graylog Our last tool but by no means the least is Graylog. It is a log management platform that gathers data from different locations across your network infrastructure.

It is worth a look considering its great scalability, user-friendly interface and great functionality.

Graylog’s great features include;

  • Customizable dashboards allowing you to choose what metrics or data sources you will monitor and analyze.
  • Built-in fault tolerance that can run multi-threaded searches to analyze several potential threads together.

All these tools have the basic and fundamental capabilities of Security Information and Event Management and these are Log collection, Normalization, Notifications and Alerts, Threat Incident Detection and Incident response.

As open-source tools, they are available for the public to use as is, while some are flexible and modifications can be made.

However, it is generally expected that free tools will not offer as much value as the paid options especially for enterprise-level usage but are a great option to try out for the start and as your organization’s security needs grow, you have the paid options to turn to.

If you enjoyed this article on the best open source SIEM tools but want to find out more on SIEM? Then look no further than our dedicated guide on what exactly is SIEM?

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