In today's digitally interconnected world, securing information systems is paramount. One key defensive strategy is detecting unauthorized changes in the file system, which can be indicative of an attack or the presence of malicious software. AIDE (Advanced Intrusion Detection Environment) provides a powerful tool for Unix-like systems, including CentOS, offering advanced capabilities for detecting such changes. In this article, we'll explore how to implement AIDE on CentOS 7.

Introduction to AIDE

AIDE is an intrusion detection tool that operates on the principle of file checksums and file attribute database checks on disk. It allows administrators to identify when changes have occurred to files or configuration settings, often serving as the first sign of system compromise.

Prerequisites

Before you begin installing and configuring AIDE on CentOS 7, ensure you have:

• Access to root or a user with sudo privileges.
• Basic knowledge of working in the terminal.
• An updated system (use sudo yum update and sudo yum upgrade commands).

Installing AIDE

1. Installing the AIDE package: Begin by installing AIDE using the yum package manager. Open a terminal and run the following command:

   sudo yum install aide
   ​

2. Initializing the AIDE database: After installation, you need to create an initial database, which will serve as the reference point for future checks. Do this by running:

   sudo aide --init
   ​

   The created database will be located at /var/lib/aide/aide.db.new.gz. Move it to the correct location and rename it using:

   sudo mv /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
   ​

Configuring AIDE

AIDE is highly configurable, meaning you can specify which files and directories to monitor, what file attributes to check, and so on. The configuration file for AIDE is located at /etc/aide.conf.

1. Editing the configuration file: Use your favorite text editor to modify /etc/aide.conf. Here, you can define rules for monitoring specific files or directories. For example, to monitor changes in /etc, you can add:

   /etc Normal
   ​

2. Monitoring rules: The rules in aide.conf specify which file attributes to check. For example, the Normal rule may include checking permissions, inodes, link counts, user, group, size, checksum, etc.

 

Regularly Checking for Changes

After setting up AIDE, it's important to regularly perform checks to identify unauthorized changes. This can be done manually by running:

sudo aide --check

This command compares the current state of the file system with the AIDE database. Any differences will be reported, and it's up to the administrator to determine whether the changes are legitimate or signs of intrusion.

To automate this process, you can create a cron job that regularly executes aide --check.

 

Implementing AIDE on CentOS 7 is a crucial step in securing the file system against unauthorized changes. With regular checks and thorough configuration, AIDE can provide a valuable layer of protection for your system. However, it's important to recognize that no tool is 100% reliable and should be used as part of a broader security strategy.