OSSEC

OSSEC manages host-based intrusion detection and system monitoring by providing a comprehensive, open-source solution. At its core, OSSEC combines host-based intrusion detection (HIDS), log monitoring, and security information and event management (SIEM) capabilities into a single, powerful platform.

The technical architecture of OSSEC involves a centralized manager (or server) that coordinates with agents installed on the systems to be monitored. These agents can be deployed on a wide range of platforms, including Linux, Windows, macOS, and various Unix variants. The manager collects and analyzes logs, performs file integrity monitoring (FIM), detects rootkits and malware, and implements active response mechanisms such as firewall policy changes and self-healing actions.

Operationally, OSSEC requires careful configuration to ensure effective monitoring and response. Key considerations include ensuring network connectivity between the manager and agents, configuring firewalls to allow necessary communication, and managing the authentication process using the ossec-authd service on the server and the agent-auth client on the agents. Additionally, OSSEC's log analysis engine can handle multiple log formats and correlate events in real-time, though this can introduce performance overhead as the volume of logs increases.

From a technical standpoint, OSSEC is written in C and operates under the GNU GPL v2 license. It supports various compliance standards such as PCI-DSS and NIST, and it maintains a forensic copy of system changes over time. The system inventory feature collects detailed information about the monitored systems, including software, hardware, and network services. However, the complexity of the setup and the need for continuous rule updates and configuration adjustments can be limiting factors, especially in large-scale deployments.