Strengthening Network Security with Zeek: A Practical Guide for Threat Detection

As cyber threats grow in complexity, the need for effective network monitoring has never been more critical.

Analyzing network traffic plays a vital role in identifying suspicious behavior, supporting incident response, and maintaining overall system integrity. One particularly effective solution for this task is Zeek (previously known as Bro), a powerful open-source framework for network traffic analysis.

This article offers a hands-on overview of Zeek—covering its installation, key features, and use in real-world threat hunting scenarios.

Understanding Zeek: A Tool Built for Security Professionals

Zeek operates as a network security monitor, designed to provide deep visibility into network traffic. It goes beyond traditional intrusion detection systems by logging detailed network activity, which can be used to identify trends, investigate anomalies, or even reconstruct attacks.

Notable Capabilities:

• Real-Time and Retrospective Analysis: Compatible with both live network streams and previously captured traffic (PCAPs).

• Comprehensive Logging: Produces rich datasets from protocols like HTTP, DNS, SSH, and more.

• Efficient Performance: Can be deployed on standard hardware, making it accessible to organizations of all sizes.

• Highly Customizable: Modular architecture allows analysts to write custom detection scripts and analyzers.

• Broad Use Cases: Supports a range of security operations, from monitoring and threat hunting to forensic analysis.

How to Install Zeek

Setting up Zeek is relatively simple, with support across major operating systems.

For macOS:

For Ubuntu/Debian Linux:

Once installed, Zeek is ready to analyze traffic either in real time or from recorded files.

Analyzing Traffic with Zeek

To begin exploring traffic data from a capture file:

This command produces a variety of log files, each offering a different lens into your network’s behavior.

Overview of Zeek Log Files

Zeek’s output is organized into structured log files that provide in-depth visibility:

• con.log: Summarizes connection metadata—IP addresses, ports, protocols, and durations.

• http.log: Contains HTTP request/response data, user-agent strings, and target URLs.

• dns.log: Logs DNS activity to help identify domain-based threats.

• ssh.log: Tracks SSH connections to detect brute-force or unauthorized access attempts.

• ftp.log: Captures FTP sessions, useful in identifying data exfiltration or unapproved transfers.

• dpd.log: Helps recognize protocols running on unexpected ports.

• modbus.log, dnp3.log: Monitors industrial control protocols for vulnerabilities or anomalies in critical infrastructure.

Why Zeek Is Critical for Threat Hunting

Zeek is not just a monitoring tool—it’s an intelligence platform. Here’s how it supports security teams:

• Comprehensive Visibility: Each connection has a unique identifier (UID), enabling cross-referencing between different logs.

• Anomaly Detection: Unusual traffic patterns become easier to spot through detailed records.

• Custom Scripting: Analysts can create tailored scripts to monitor specific behaviors, protocols, or threat indicators.

Integrating Zeek with Broader Security Frameworks

Pairing Zeek with Open Network Detection and Response (Open NDR) solutions and aligning your detection logic with the MITRE ATT&CK framework greatly improves security operations. This combination provides structured detection capabilities and accelerates response times by aligning observable activity with known adversarial techniques.

Optimizing SOC Operations: Addressing SMB Protocol Gaps

Security teams often struggle with SMB (Server Message Block) protocol visibility. Zeek can help bridge this gap by capturing critical SMB metadata, improving alert accuracy and providing deeper insights into lateral movement within the network.

Conclusion

Zeek offers a flexible and robust approach to network monitoring, making it a valuable asset for security analysts and SOC teams alike. Its detailed logging, extensibility, and compatibility with industry frameworks empower teams to stay ahead of emerging threats and respond effectively.

Get Started with Zeek

If you’re looking to enhance your network defense strategy, Zeek is a strong starting point. Explore its features, customize its behavior to suit your infrastructure, and integrate it into your threat detection stack for improved situational awareness.

For expert guidance, check out insights from cybersecurity leaders like Dan Gunter, CEO of Insane Cyber, who discuss real-world applications of Zeek in enterprise environments. Watch the full video here.