In 2025, Security Information and Event Management (SIEM) tools are critical for cybersecurity operations. They help organizations detect, investigate, and respond to security threats by aggregating and analyzing log data. Open-source SIEM tools offer robust functionality at no cost, making them ideal for SMBs and enterprises looking to enhance their security posture without breaking the bank.

Below, we explore the top 10 open-source SIEM tools, detailing their features, pros, cons, use cases, and ratings to help you choose the best one for your organization.

Wazuh
Wazuh is an open-source security platform offering SIEM, XDR, and compliance capabilities. It provides real-time threat detection, vulnerability assessment, and intrusion monitoring, making it ideal for enterprise-level security.

✅ Features:
Threat Detection: Monitors system activities for malicious behavior and suspicious anomalies.
File Integrity Monitoring (FIM): Detects changes in critical files and directories.
Log Analysis: Aggregates logs from various sources for centralized monitoring.
Host-Based Intrusion Detection (HIDS): Identifies unauthorized access or suspicious activities.
Regulatory Compliance: Ensures adherence to GDPR, HIPAA, and PCI DSS standards.
Elastic Stack Integration: Seamless compatibility with Elasticsearch, Logstash, and Kibana for advanced visualization.
👍 Pros:
Comprehensive security monitoring with detailed log analysis.
Highly scalable and suitable for large enterprises.
Extensive documentation and active community support.
👎 Cons:
Steeper learning curve for new users.
Resource-intensive during large-scale deployments.
🛠️ Best for: Enterprise environments needing scalable, open-source threat detection and compliance monitoring.
⭐ Rating: 4.6/5
2. AlienVault OSSIM
AlienVault OSSIM (Open Source Security Information Management) is a SIEM platform developed by AT&T. It offers unified security monitoring with built-in asset discovery, vulnerability assessment, and event correlation.

✅ Features:
Asset Discovery: Automatically identifies and maps network assets.
Threat Intelligence: Leverages AT&T Alien Labs’ threat intelligence feed.
Real-time Event Correlation: Analyzes log data to detect suspicious patterns.
Vulnerability Scanning: Assesses network vulnerabilities with regular scans.
Compliance Management: Supports GDPR, HIPAA, and PCI DSS compliance.
👍 Pros:
All-in-one security platform with multiple integrated tools.
User-friendly interface for easier management.
Continuous updates with latest threat intelligence.
👎 Cons:
Limited scalability for large organizations.
Resource-heavy and requires frequent updates.
🛠️ Best for: SMBs seeking a free, all-in-one security solution with built-in vulnerability scanning.
⭐ Rating: 4.4/5
3. Security Onion
Security Onion is a Linux-based open-source SIEM and threat-hunting platform. It is widely used for enterprise security monitoring, log management, and network intrusion detection.

✅ Features:
Full-Packet Capture: Captures and inspects network traffic in real-time.
Log Management: Aggregates logs from multiple sources.
Threat Hunting: Includes tools like Zeek, Suricata, and Elasticsearch.
Customizable Dashboards: Built-in dashboards for security monitoring.
Incident Response: Automated alerting and correlation.
👍 Pros:
Comprehensive security suite with multiple integrated tools.
Fast deployment with easy installation scripts.
Active community support and regular updates.
👎 Cons:
High system resource consumption.
Complex setup for large-scale environments.
🛠️ Best for: Enterprises looking for an all-in-one solution for threat hunting and intrusion detection.
⭐ Rating: 4.5/5
4. Elastic SIEM
Elastic SIEM is part of the Elastic Stack (ELK) and offers real-time security monitoring and threat detection. It is known for its scalability and advanced analytics capabilities.

✅ Features:
Data Ingestion: Collects and processes large volumes of security data.
Kibana Visualization: Powerful data visualization and custom dashboards.
Real-time Threat Detection: Uses machine learning models for anomaly detection.
Alerting: Configurable alerting with detailed incident reports.
Open-source integrations: Compatible with Beats, Logstash, and Elasticsearch.
👍 Pros:
Highly scalable and suitable for large organizations.
Advanced data visualization capabilities.
Built-in machine learning for anomaly detection.
👎 Cons:
Resource-intensive.
Requires external components for full SIEM functionality.
🛠️ Best for: Large enterprises with complex data analysis and monitoring needs.
⭐ Rating: 4.7/5
5. Graylog
Graylog is a centralized log management and SIEM platform. It offers powerful log analysis, event correlation, and real-time alerting.

✅ Features:
Centralized Log Management: Aggregates logs from multiple sources.
Real-time Event Correlation: Detects security incidents quickly.
Custom Dashboards: Advanced data visualization.
Flexible Query Language: Simplifies search operations.
User Access Control: Role-based access permissions.
👍 Pros:
User-friendly interface with customizable dashboards.
High-speed data processing for large environments.
Extensive plugin support.
👎 Cons:
Limited threat intelligence.
Advanced features require enterprise license.
🛠️ Best for: Medium to large organizations needing scalable log management with SIEM capabilities.
⭐ Rating: 4.3/5
6. SIEMonster
SIEMonster is a modular open-source SIEM solution offering log management, event correlation, and incident response.

✅ Features:
Log Ingestion: Collects logs from multiple sources.
Custom Dashboards: Real-time data visualization.
Event Correlation: Automated event aggregation and analysis.
Incident Response: Automated alerting and threat mitigation.
Threat Intelligence: Third-party integration support.
👍 Pros:
Highly customizable and flexible.
Free community edition available.
Suitable for small and large deployments.
👎 Cons:
Limited documentation.
Complex configuration for advanced use cases.
🛠️ Best for: Enterprises seeking a customizable SIEM platform.
⭐ Rating: 4.2/5
7. OSSEC
OSSEC is a lightweight, host-based intrusion detection system (HIDS) with SIEM capabilities.

✅ Features:
File Integrity Monitoring: Detects changes in critical files.
Rootkit Detection: Identifies and prevents rootkits.
Log Analysis: Analyzes system logs for suspicious activity.
Real-time Alerts: Immediate notification of potential threats.
Agent-based monitoring: Covers endpoints effectively.
👍 Pros:
Low resource usage.
Effective intrusion detection.
Free and open-source.
👎 Cons:
No built-in GUI.
Limited scalability.
🛠️ Best for: SMBs needing a lightweight HIDS solution.
⭐ Rating: 4.0/5
Conclusion
Open-source SIEM tools provide cost-effective solutions for threat detection, log management, and compliance monitoring. Wazuh, Elastic SIEM, and Security Onion stand out for their comprehensive security features and scalability, while AlienVault OSSIM and Graylog offer strong event correlation and visualization capabilities. Choosing the right SIEM depends on your organization's size, infrastructure, and security requirements.

Reference : www.worksent.com