Is OSSEC open source?

Yes. OSSEC is open source under the GPL-2.0 licence. Its source code is on GitHub at ossec/ossec-hids and is written mainly in C.

Yes. OSSEC is open source, so the software itself is free to use.

Can I self-host OSSEC?

Yes. OSSEC can be self-hosted on your own server or infrastructure.

What is OSSEC an alternative to?

OSSEC is an open-source alternative to CrowdStrike, SentinelOne, Microsoft Defender and Kaspersky. Other open-source alternatives to CrowdStrike include Wazuh, Security Onion and Falco.

Is OSSEC actively maintained?

Yes. The most recent commit to OSSEC was on 17 September 2026, and the latest release is 4.3.0, published on 25 August 2026. The project has 5.1k stars on GitHub.

OSSEC: open-source alternative to CrowdStrike, SentinelOne

About OSSEC

OSSEC is a host-based intrusion detection system (HIDS) that watches individual servers and endpoints for signs of compromise. Its README describes it as a platform that brings together HIDS, log monitoring and SIM/SIEM capabilities in one open-source package.

The project's description lists log analysis, file integrity checking, policy monitoring, rootkit detection, real-time alerting and active response. Those capabilities support compliance work as well as detection, and the repository's topics refer to PCI DSS and NIST 800-53. Stable releases and documentation are published on ossec.net, with community help on Slack and Discord.

OSSEC is written in C and licensed under GPL-2.0. It bundles a modified zlib and a small part of OpenSSL, along with the cJSON library. Atomicorp hosts the annual OSSEC conference, and the development version is available through a simple git clone.

Key features

Host-based intrusion detection
Log analysis and monitoring
File integrity monitoring
Policy monitoring
Rootkit detection
Real-time alerting and active response

Good fit for

→Monitoring servers for tampering
→Supporting compliance-driven file integrity monitoring

Built with: C
Tags: hids; intrusion-detection; security; file-integrity; log-analysis; siem; compliance; rootkit-detection

OSSEC: questions and answers

What is OSSEC used for?: OSSEC is an open-source host-based intrusion detection system that combines log analysis, file integrity checking, rootkit detection, real-time alerting and active response. It is a good fit for monitoring servers for tampering and supporting compliance-driven file integrity monitoring.
Is OSSEC open source?: Yes. OSSEC is open source under the GPL-2.0 licence. Its source code is on GitHub at ossec/ossec-hids and is written mainly in C.
Is OSSEC free?: Yes. OSSEC is open source, so the software itself is free to use.
Can I self-host OSSEC?: Yes. OSSEC can be self-hosted on your own server or infrastructure.
What is OSSEC an alternative to?: OSSEC is an open-source alternative to CrowdStrike, SentinelOne, Microsoft Defender and Kaspersky. Other open-source alternatives to CrowdStrike include Wazuh, Security Onion and Falco.
Is OSSEC actively maintained?: Yes. The most recent commit to OSSEC was on 17 September 2026, and the latest release is 4.3.0, published on 25 August 2026. The project has 5.1k stars on GitHub.