File Integrity Monitoring with AIDE And Tripwire

File Integrity Monitoring (FIM) is a crucial security process that detects unauthorized changes to files and directories on a Linux system. This practice helps identify intrusions, system misconfigurations, or malicious activities by continuously verifying the integrity of critical files. Tools like AIDE (Advanced Intrusion Detection Environment) and Tripwire are among the most widely used FIM solutions, providing automated detection through cryptographic checksums and detailed reporting.

Understanding File Integrity Monitoring

FIM tools create a baseline by calculating and storing cryptographic hashes (MD5, SHA-256, etc.) of files and directories. They periodically scan the system comparing current file states with the stored baseline. Any unauthorized additions, modifications, or deletions trigger alerts, enabling timely investigation and response.

Importance of FIM

1. Detects subtle unauthorized changes that may bypass other security mechanisms.

2. Supports compliance requirements for PCI DSS, HIPAA, and GDPR.

3. Enhances system reliability by monitoring configuration files and critical binaries.

AIDE (Advanced Intrusion Detection Environment)

AIDE (Advanced Intrusion Detection Environment) is an open-source, lightweight file integrity checker used to monitor unauthorized changes to files and directories. It supports multiple hash algorithms and offers detailed, rule-based configuration for flexible and precise monitoring. Due to its simplicity and efficiency, AIDE is ideal for periodic integrity checks and quick deployment in security-sensitive environments.

Installation and Initialization

1. Install using package managers (yum install aide or apt-get install aide).

2. Create a database of file signatures with:

3. Replace the initial database:

Running Integrity Checks

1. Execute periodic scans:

2. Review output for discrepancies and generate detailed reports.

3. Automate scans via cron jobs for continuous monitoring.

Configuration File Highlights

1. Located in /etc/aide.conf.

2. Define directories and files to monitor.

3. Specify attributes and hash functions (e.g., SHA256, read permissions, inore file size).

4. Example rule snippet:

Tripwire

Tripwire is a file integrity monitoring solution available in both open-source and commercial editions. It offers extensive configuration options along with enterprise-level reporting capabilities, making it suitable for larger and more complex environments. Tripwire uses cryptographic hash functions to detect unauthorized changes to files and ensure system integrity.

Installation and Setup

1. Install via package manager.

2. Initialize database with:

3. Configure policy and configuration files located in /etc/tripwire/.

4. Update and manage policies using twadmin.

Performing Checks

1. Run integrity checks with:

2. Examine generated reports for alerts on changes.

3. Supports integration with SIEM systems for centralized monitoring.