File Integrity Monitoring (FIM) is a crucial security measure that helps detect unauthorized changes to files and directories, ensuring the integrity and security of your system. While FIM is commonly associated with enterprise environments and often implemented using specialized software, macOS provides native tools and third-party solutions that can be adapted for this purpose. This article will guide you through setting up FIM on macOS using built-in tools and open-source software.

Examples:

Using Built-in Tools: fs_usage and auditd

1. Monitoring File Access with fs_usage

fs_usage is a command-line tool that can monitor file system operations in real-time. It is useful for observing which processes are accessing or modifying files.

Example Command:

sudo fs_usage -w | grep "open"

This command will display real-time file access events where files are being opened.

2. Using auditd for Comprehensive Monitoring

auditd is a powerful auditing daemon available on macOS that can be configured to monitor file integrity.

Step-by-Step:

1. Enable the Audit Framework:

   sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.auditd.plist

2. Configure Audit Rules: Edit the audit configuration file located at /etc/security/audit_control to include rules for monitoring specific files or directories. For example:

   dir:/path/to/monitor flags:all

3. Restart auditd:

   sudo audit -s

4. Review Audit Logs: Audit logs are stored in /var/audit/. You can review them using:

   sudo praudit /var/audit/current

Using Open-Source Software: ossec

ossec is an open-source host-based intrusion detection system (HIDS) that includes file integrity monitoring capabilities.

Installation and Configuration:

1. Install ossec:

   brew install ossec

2. Configure ossec: Edit the ossec.conf file located at /usr/local/etc/ossec.conf to specify the directories and files you want to monitor. Example configuration:

   <syscheck>
    <directories check_all="yes">/path/to/monitor</directories>
   </syscheck>

3. Start ossec:

   sudo /usr/local/ossec/bin/ossec-control start

4. Review Alerts: ossec will generate alerts and logs in the /usr/local/ossec/logs/alerts/ directory.