How to Create Effective Wazuh Rules

Wazuh is a powerful open-source threat detection and security monitoring platform. Creating custom rules is vital for tailoring Wazuh to meet specific security requirements. This tutorial provides a detailed guide on crafting effective Wazuh rules.

Prerequisites

Basic understanding of security monitoring concepts and terminologies.
Access to a Wazuh server with administrative privileges.
Text editor (preferably one with syntax highlighting).

Understanding Wazuh Rules

Wazuh rules are XML-structured files that define patterns to detect anomalies or malicious activities within your environment. These rules operate within the Wazuh Manager and trigger alerts when criteria are met.

Structure of a Wazuh Rule

Rule ID: A unique identifier for the rule.
Alert Level: The severity of the alert generated by this rule.
Group: Categorizes the rule under a specific group for easier management.
Description: A brief narrative of the rule’s purpose.
Conditions: Specify the log patterns or conditions that trigger the rule.

Creating a Custom Wazuh Rule

Access the Rules Directory: Open your terminal and navigate to the Wazuh rules directory, typically found at /var/ossec/rules.
Create a New Rule File: Use your preferred text editor to create a new XML file, for example, my_custom_rules.xml.

Define Your Rule: Use the following template to define your rule:

<group>my_custom_rules_group</group>
<rule id="100001" level="5">
   <decoded_as>json</decoded_as>
   <description>Custom rule for detecting specific failed login attempts</description>
   <group>authentication_failures</group>
   <match>Failed password for invalid user</match>
</rule>

Integrate the Rule: Save and close the file. Then, edit the main rules configuration file to include your custom rules file by adding its path.
Restart the Wazuh Manager: Apply your changes by restarting the Wazuh Manager using the command systemctl restart wazuh-manager.

Troubleshooting and Validating Rules

Use ossec-logtest to test your rule syntax and functionality before deploying widely.
If alerts are not generated, double-check the match conditions and ensure log data compatibility.
Consult the Wazuh documentation for examples and guidelines on crafting complex conditions.

For additional security configurations, check out our guide on installing Wazuh SIEM.

Summary Checklist

Understand the basic structure and components of a Wazuh rule.
Create and define a new rule within the correct directory.
Test and validate the rule before applying it in a live environment.
Integrate your custom rule into the Wazuh configuration and restart the manager.
Use available tools to ensure rule efficacy and response accuracy.