What is File Integrity Monitoring (FIM)?

File integrity monitoring definition

File integrity monitoring (FIM) is a security process for continuously monitoring and detecting changes made to sensitive files, such as file systems, databases, directories, application files, and operating systems, for signs of suspicious behavior as a way of discovering potential cyberattacks.

FIM, which is sometimes called file integrity management, helps organizations determine the integrity of their systems and applications through changes made to critical files. This includes what accounts made the changes, how they were altered, and whether these actions were malicious.

Alongside speeding up cyberattack discovery, FIM helps organizations find and close security gaps created through unintentional file changes. Additionally, FIM enables security teams to conduct forensics analysis following incidents to understand where threat actors got through defenses, who might be responsible for the incident, and how to prevent a similar attack in the future.

Traditional FIM can be agent based or agentless. Agent-based FIM involves installing agents, which enables deeper visibility in real time but is more resource intensive. Agentless FIM doesn’t require as many resources, but only captures a snapshot of the file system changes. If anything happens between scans, security teams will be slower to respond.

This has led to the emergence of advanced FIM solutions that continuously monitor at runtime. The newer advanced FIM tools are more adept at monitoring complex cloud environments, including containers and Kubernetes.

Organizations can adopt discrete FIM tools, but many cloud security solutions include FIM features, such as security posture management (CSPM) tools, cloud-native application protection platforms (CNAPP) that include CSPM capabilities, and runtime security solutions.

Why file integrity monitoring is important

FIM is an important cybersecurity technology because it alerts security teams when critical files have been tampered with, which could imply a cyberattack. It can also detect advanced techniques, like malware utilization of temporary files used to obfuscate attacks. Afterwards, FIM detections enable security teams to perform digital forensics analysis to investigate the attack or incident.

FIM can help organizations comply with regulations and standards, such as HIPAA, PCI DSS, GDPR, and more. Many regulations require ensuring the protection of critical files, and FIM provides alerts when anything changes from the expected baseline.

For example, PCI DSS Requirement 11.5 explicitly calls for the use of FIM to provide a change detection mechanism for compliance. For GDPR compliance, Article 32 requires organizations to maintain the integrity of personal data.

Benefits of file integrity monitoring

Alongside helping organizations discover cyberattacks through file changes and ensuring regulatory compliance, FIM benefits include:

• Understand the entire attack surface. As organizations migrate to more complex cloud deployments, security gaps arise that FIM tools can help security teams find through file system changes.
• Creates an auditable environment. FIM solutions create detailed audit trails organizations can use to ensure they are compliant with relevant regulations.
• Detecting threats quicker. While legacy FIM tools provide slower, scheduled snapshots of critical files, advanced FIM solutions provide continuous monitoring so security teams know immediately whether a critical file deviates from expected behavior.

Challenges of file integrity monitoring

Implementing file integrity monitoring solutions is not without challenges that security teams need to tackle, including:

• Alert fatigue. If too many file systems are in scope and the detection methodology is broad, then security teams may be inundated with too many alerts, which can result in missing critical incidents and wasted time investigating each issue.
• Resource heavy. Traditional FIM can often require more compute resources to run scans because it often scans everything, which can be both wasteful and potentially impact IT systems’ performance.
• Snapshot insight. Some FIM tools only perform scheduled scans of file changes, which can limit context around any changes discovered and allow attacks done between scans to slip through, as well as cover their tracks.
• Scalability. Keeping up with the growing volume of files and increasingly complex IT environments means that organizations need to be sure their FIM solution can scale up appropriately, or file changes could be missed. Ways to address it include using agent-based FIM on the resource or a runtime FIM solution.
• Insider threats. Traditional FIM monitors for unapproved or suspicious changes, which means that changes made by malicious insiders with approved permissions could go unnoticed or require the implementation of additional FIM policies.

How file integrity monitoring works

The first step involves security teams defining the FIM policies to identify which file systems are in scope for monitoring.

From there, FIM tools create an initial baseline of current file configurations for which to compare potential changes against during scans or while listening to file system events at runtime. A baseline inventory involves the creation of cryptographic hashes for all in-scope file systems. File changes will result in a changed hash to make comparison easier.

With a baseline collected, FIM solutions then monitor changes made to files. Some FIM tools perform periodic and scheduled scans to compare baseline stored hashes against the current file hashes. Advanced FIM solutions can continuously monitor for file changes during runtime.

If an unapproved change is detected, the FIM solution can generate an alert for security teams to follow up and investigate. Some tools have automated response capabilities, such as pausing, quarantining, or killing a container with detected file changes.

Lastly, FIM solutions generate reports so organizations can prove compliance with relevant regulations.

File integrity monitoring best practices

The following are some FIM best practices to implement:

1. Define a baseline and appropriate permissions. Alongside the asset inventory, organizations should create a baseline to know when a file has deviated or drifted from the expected baseline, and when file access is suspicious.
2. Use automated alert and response mechanisms. Security teams are often buried in alerts. Having remediation responses, such as predefined workflows or automations, in runtime policies can help stop an attack in the event a FIM alert is initially overlooked or missed.
3. Collect forensics data for investigation. Understanding how an attack occurred is important to preventing a similar one from happening again.
4. Follow compliance requirements. To ensure the organization remains compliant with relevant regulations, learn which files need to be monitored, such as log files, and include that in the asset inventory.
5. Implement runtime policies. Advanced FIM solutions offer detection policies for runtime, which can create alerts should any suspicious file changes occur, strengthening security posture.

Get advanced file integrity monitoring with Sysdig Secure

Protecting critical file systems is an integral part of any cybersecurity strategy. Traditional FIM can lack the context needed around file changes or create an avalanche of alerts that swamps your security team.

With Sysdig runtime FIM, which leverages Falco, you get a lightweight, fast, and context-rich FIM solution that monitors critical file paths in real time and triggers only if a file has been written to and the hash doesn’t match. 

Sysdig advanced runtime FIM provides forensics details for faster investigations, preserves system performance, reduces mean time to containment, and meets compliance requirements without the complexity of legacy tools. Learn more about Sysdig runtime FIM here.

Ready to modernize your FIM strategy? Request a demo to see Sysdig FIM in action.