Security Onion

Security Onion is a free and open-source Linux distribution for intrusion detection, network security monitoring (NSM), and log management. It’s widely used in Security Operations Centers (SOCs), cybersecurity training labs, and enterprise monitoring setups.

Developed and maintained by Doug Burks and the Security Onion team, it provides an integrated suite of tools like Snort, Suricata, Zeek, Wazuh, and Elasticsearch — all preconfigured for rapid deployment.

Why Security Onion?

Security Onion simplifies complex security infrastructure into a single, cohesive platform.

In simple terms:

Security Onion collects, inspects, and visualizes network data — helping analysts detect, investigate, and respond to security threats efficiently.

Core Components

Component	Description
Snort / Suricata	Network Intrusion Detection Systems (IDS/IPS)
Zeek (formerly Bro)	Network analysis framework for protocol and behavior-based detection
Wazuh / OSSEC	Host-based intrusion detection (HIDS) and log analysis
Elastic Stack (ELK)	Elasticsearch, Logstash, and Kibana — for storing and visualizing logs
TheHive + Cortex	Incident response and case management
CyberChef	Data decoding, conversion, and analysis tool

Architecture Overview

This architecture allows real-time traffic inspection, data correlation, and security event visualization from a single pane of glass.

Installation Modes

Security Onion supports three main deployment modes:

Mode	Use Case
Standalone	Ideal for labs and small networks
Distributed	For enterprise-scale environments with multiple sensors
Eval Mode	Quick evaluation using a single VM (best for beginners)

sudo so-setup

You can select the desired mode during setup and configure sensors, managers, and storage accordingly.

Workflow: From Detection to Response

This flow demonstrates how Security Onion provides end-to-end visibility, from detection → analysis → investigation → response.

Log Correlation Formula

To understand correlation mathematically, think of Security Onion’s detection engine as:

$$A(t) = \sum_{i=1}^{n} (E_i \times W_i)$$

Where:

• $A(t)$: Alert strength at time t
• $E_i$: Event score (based on severity, frequency, or signature match)
• $W_i$: Weight of event importance

Higher $A(t)$ indicates higher confidence of a real incident — enabling analysts to prioritize critical alerts efficiently.

Real-World Use Cases

Scenario	Description
SOC Operations	Centralized log management and real-time threat monitoring
Threat Hunting	Searching for Indicators of Compromise (IOCs) and anomalies
Incident Response	Using TheHive to manage and document security incidents
Training Labs	Perfect for blue team exercises and cyber range setups

Key Tools Inside Security Onion

• so-status — Check system and service health
• so-allow — Manage firewall rules and IP access
• so-import-pcap — Import and analyze captured network traffic
• so-query — Query Elasticsearch directly from the terminal
• so-dashboard — Manage and monitor dashboard views

sudo so-import-pcap /path/to/traffic.pcap

This command imports and indexes network captures into the Elastic Stack for retrospective analysis.

Integration with SIEM and EDR

Security Onion can send data to external systems like:

• Splunk
• Microsoft Sentinel
• Wazuh EDR
• Graylog
• ArcSight

This allows hybrid monitoring and advanced analytics across diverse environments.

Key Takeaways

• Security Onion is an all-in-one platform for IDS, NSM, and log management.
• Combines Snort/Suricata, Zeek, Elastic Stack, Wazuh, and TheHive.
• Perfect for SOC environments, blue team training, and incident response.
• Supports distributed deployments for scalability.
• Offers real-time dashboards and correlation across multiple data sources.