Why Consider an Open-Source SIEM?
Security Information and Event Management (SIEM) platforms are central to any mature security operations capability. They aggregate logs, correlate events, generate alerts, and support incident investigations. Commercial SIEMs can carry significant licensing costs, making open-source alternatives an attractive option for budget-conscious organizations, small teams, or those who need a development/lab environment.
Three of the most widely adopted open-source (or source-available) SIEM solutions are Wazuh, Graylog, and OpenSearch Security Analytics. Each has distinct strengths and trade-offs.
Wazuh
Wazuh is a free, open-source security platform that evolved from OSSEC. It combines host-based intrusion detection (HIDS), log management, vulnerability detection, and compliance reporting in a single unified platform.
Key Strengths
- Agent-based endpoint monitoring with deep host visibility
- Built-in rules for MITRE ATT&CK, PCI DSS, HIPAA, and GDPR
- Active response capabilities — can automatically block IPs or kill processes
- File integrity monitoring (FIM) out of the box
- Integrates natively with OpenSearch or Elastic for visualization
Limitations
- Requires Elasticsearch/OpenSearch backend, adding infrastructure complexity
- Alert tuning and rule customization have a steep learning curve
- Best suited for endpoint-centric environments
Graylog
Graylog is a centralized log management platform with SIEM capabilities. Its open-source edition focuses on log collection, parsing, and search, while its Security edition adds correlation rules and anomaly detection.
Key Strengths
- Excellent log ingestion pipeline — supports syslog, GELF, Beats, and more
- Powerful query language for interactive log investigations
- Clean, intuitive web interface
- Strong community and extensive plugin ecosystem
- Scales well horizontally for high log volume environments
Limitations
- Advanced SIEM features (correlation, behavioral analytics) require the commercial Security tier
- MongoDB and Elasticsearch dependencies add operational overhead
- Native threat intelligence integration is limited in the open-source edition
OpenSearch Security Analytics
OpenSearch is Amazon's open-source fork of Elasticsearch, and its Security Analytics plugin adds SIEM-grade detection capabilities directly within the OpenSearch ecosystem.
Key Strengths
- Native integration with OpenSearch Dashboards for visualization
- Sigma rule support — leverage the community's massive detection rule library
- Findings and alerts correlation without additional tooling
- No licensing cost; fully open-source under Apache 2.0
- Cloud-friendly — runs on AWS OpenSearch Service or self-hosted
Limitations
- Security Analytics plugin is relatively newer and still maturing
- Requires comfort with the OpenSearch/Elastic stack
- Less out-of-the-box compliance reporting compared to Wazuh
Side-by-Side Comparison
| Feature | Wazuh | Graylog (OSS) | OpenSearch SA |
|---|---|---|---|
| Endpoint Monitoring | ✅ Strong | ⚠️ Limited | ⚠️ Limited |
| Log Management | ✅ Good | ✅ Excellent | ✅ Good |
| Detection Rules | ✅ Built-in | ⚠️ Commercial | ✅ Sigma |
| Compliance Reports | ✅ Built-in | ⚠️ Limited | ❌ Minimal |
| Ease of Setup | Moderate | Moderate | Moderate |
| Cost | Free | Free (OSS) | Free |
Which Should You Choose?
Choose Wazuh if your primary need is endpoint security monitoring, compliance reporting, and host-based detection. Choose Graylog if log aggregation, search, and operational visibility are your focus and you don't need deep correlation out of the box. Choose OpenSearch Security Analytics if you are already in the OpenSearch/Elastic ecosystem and want to leverage Sigma rules for network and cloud detection.
Many mature organizations ultimately run two of these in tandem — for example, Wazuh for endpoint telemetry feeding into OpenSearch for centralized analysis.