What is File Integrity Monitoring (FIM)
File Integrity Monitoring (FIM) is the process of monitoring files in a system to identify file creation, modification, and deletion. It is commonly used to detect when sensitive or critical system files and configurations are altered without authorization. It serves as an auditing system for files to detect who made changes to the file, what changes were made, and when the changes were made.
FIM, when integrated with other security tools, acts as an early warning mechanism that detects signs of cyberattacks, such as malware being added to a monitored directory. It contributes to the security defense layer for organizations to monitor their sensitive assets.
How File Integrity Monitoring works
File integrity monitoring (FIM) identifies modifications, creations, or deletions of files. Files and directories are monitored for changes, tracking attributes, permissions, ownership, size, and content.
Below we discuss some of the file changes monitored by FIM.
File creation
FIM identifies newly created files by comparing the current state of a monitored directory with its previous state, detecting any additions. It logs details such as the file name, hash value, creation timestamp, the user responsible, and the associated process. FIM stores the file attributes in a local FIM database when the file is created.
File modification
FIM looks for file modifications by comparing the latest checksum value of a file to the already stored checksum and attribute values. If the latest checksum value does not match the previously stored checksum value, an alert is generated, indicating a modification in the file.
File deletion
If a file that was present in the monitored directory is missing during the latest scan, FIM recognizes it as deleted. It records information about the deleted file, including its last known attributes and the time the deletion was detected.
Applications of File Integrity Monitoring
File integrity monitoring can be applied in several ways to maintain integrity, ensure compliance, and enhance overall system security. Some applications of FIM include:
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File change auditing: FIM is essential for maintaining a proper audit trail of files within a directory. It continuously monitors sensitive or critical system and configuration files for modifications, additions, or deletions. It detects who created, modified, or deleted a file, when it was created, modified, or deleted, and what was changed during modification. Overall, it allows for complete visibility of a file's lifecycle.
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Compliance with regulatory standards: Many regulations, such as PCI DSS, HIPAA, NIST 800-53, TSC, and GDPR, require organizations to implement FIM to protect sensitive data and ensure its integrity. FIM helps meet audit requirements by providing detailed logs and reports of file changes to support accountability and transparency.
- Threat detection and response: FIM, in combination with other security tools, helps to identify potential cyberattacks like unauthorized system configuration and file changes. Such unauthorized system configuration and file changes can be major indicators of compromise (IoC). With the help of FIM, you can craft appropriate detection rules to improve your detection engineering and respond accordingly.
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Cost and damage mitigation: By identifying and addressing issues early, FIM reduces the potential cost and damages caused by data breaches, ransomware attacks, or insider threats. The cost reduction provided by FIM is essential to ensuring the resilience of the IT infrastructure.
- Operational integrity: FIM ensures that unauthorized changes to critical system files, and configurations, are detected, reducing the risk of system failures. It also identifies unintended deviations from approved configurations that could affect system performance or security.
- Integration with broader security strategies: FIM works with other security tools, such as security information and event management (SIEM) systems, intrusion detection systems (IDS), and endpoint detection and response (EDR) tools, providing a comprehensive security framework. Integrating FIM with these security tools helps to correlate file creation, modification, and deletion with broader security occurrences to detect threats.
Selecting the right FIM tool
Some considerations need to be made before selecting a file integrity monitoring tool. Below are some of the most common things to consider:
- Alignment with your needs: Choose a tool that supports your organization's specific requirements, such as monitoring critical files, meeting compliance requirements (e.g., PCI DSS, HIPAA), and addressing your security goals.
- Ease of use and integration: Select a solution that is easy to deploy, configure, and use. Ensure it integrates smoothly with your existing security tools like SIEM, making it part of a broader security strategy.
- Real-time monitoring and accurate alerts: Opt for a FIM tool that provides real-time change detection with actionable alerts while minimizing false positives. This ensures quick and efficient detection which is beneficial for protection against threats.
- Robust reporting and support: Ensure the tool offers comprehensive logs and reports for audits and compliance. Reliable vendor support and clear documentation are critical for smooth implementation and ongoing management.
Best practices for configuring FIM
For optimized FIM performance, the following practices are recommended:
- Monitor critical files: Focus on essential files and directories, such as system configurations, application binaries, and sensitive data, to prioritize files and directories that matter the most.
- Establish a baselin: Define a baseline state for files to detect unauthorized changes effectively.
- Enable real-time monitoring: Use real-time monitoring for high-priority files to quickly detect and respond to changes.
- Define alert thresholds: Configure FIM to trigger alerts only for significant changes. Use severity levels to prioritize responses and reduce alert fatigue.
- Review and fine-tune regularly: Periodically review alerts, logs, and configurations to reduce false positives and adapt to system changes.
In summary, FIM is essential for enhancing security, ensuring compliance, and maintaining reliable system operations. Incorporating file integrity monitoring (FIM) into your security architecture will improve the overall integrity and security of your systems.
Learn how Wazuh helps with file integrity monitoring (FIM) in our documentation.
