Overview of Registry Monitoring with CBFS Filter

Summary

CBRegistry is a component of CBFS Filter, an SDK and library designed for monitoring and controlling various system activities, including registry operations, filesystem operations, and the lifecycle of processes and threads. This component—available as a class, struct, or trait depending on your programming language—enables you to monitor and control all types of registry operations within your Windows applications. The article reviews the purpose, features, architecture, and applications of the CBRegistry component.

Introduction

Windows provides a mechanism that notifies interested drivers about operations with the system Registry - the centralized database of configuration information of Windows. The CBRegistry driver leverages this mechanism to make notifications and supplementary information available to user-mode processes. Applications can to observe these registry requests and take necessary actions. The actions can range from simple monitoring and logging of operations to more proactive measures, such as handling a request without further processing, modifying the request, or denying it with an error.

Filtering of registry operations plays a significant role in a plethora of scenarios:

1. Registry Monitoring and Logging
   • Purpose: Track changes to critical registry keys for compliance and auditing.
   • Scenario: An enterprise application can use CBRegistry to log all modifications to the registry entries related to security policies or application configurations. By capturing who changed what and when, administrators can maintain compliance with regulatory requirements and have a clear audit trail.
2. Real-Time Threat Detection
   • Purpose: Identify and respond to malicious activities targeting the registry.
   • Scenario: Security software can monitor registry changes to detect suspicious activities, such as the installation of malware that modifies the startup keys. Upon detecting unauthorized changes, the application can alert the user, block the modification, or automatically revert it to a previous state.
3. Configuration Management
   • Purpose: Ensure consistency in application settings across different user environments.
   • Scenario: A configuration management tool can intercept registry read/write operations to enforce specific settings across all instances of an application. If a user attempts to change a setting, the tool can either deny the change or log it for review.
4. User Activity Monitoring
   • Purpose:Analyze user behavior for enhancing user experience or troubleshooting issues.
   • Scenario: An application might intercept registry operations to collect data on user preferences or application usage patterns. This information can then be used to tailor features, provide recommendations, or diagnose performance issues.
5. Policy Enforcement
   • Purpose: Organizations that must comply with regulatory requirements can use CBRegistry to maintain an audit trail of process activity.
   • Scenario: By logging all process and thread creations and terminations, companies can create a detailed report to demonstrate compliance during audits.
6. File and Registry Operations Monitoring
   • Purpose: Implement organizational policies regarding application usage and system configuration.
   • Scenario: A corporate environment could utilize CBRegistry to restrict access to certain registry keys. For instance, if an organization wants to prevent users from modifying system policies or software installations, the application can block unauthorized access or log attempts to change these settings.
7. Software Licensing and Validation
   • Purpose: Enforce licensing agreements and prevent software piracy.
   • Scenario: Licensing systems can monitor registry entries that store licensing information. By intercepting access attempts, the application can validate licenses, check expiration dates, and deny access to unauthorized users.

What CBRegistry Offers

With CBRegistry, application developers can enhance their software with advanced features without having to dive into kernel-mode development. CBRegistry includes a pre-built kernel-mode driver and a user-mode library (available as a component, class, struct, or trait). Applications interact with the user-mode library to access the functionality, while the driver is installed just once during the application's setup. After installation, the application doesn't communicate directly with the driver.

CBRegistry can be used in Windows applications developed in C#, C++, Python, Java and Java-compatible languages (Kotlin, Scala, Groovy), Go, Rust, and Delphi.

Trackable operations

With CBRegistry, you can capture and intercept the following types of operations:

• Creating registry keys
• Opening registry keys
• Closing registry keys
• Deleting registry keys
• Renaming registry keys
• Reading security attributes of registry keys
• Modifying security attributes of registry keys
• Retrieving information about registry keys
• Updating properties of registry keys
• Enumerating subkeys of registry keys
• Enumerating values of registry keys
• Retrieving values from registry keys
• Updating values in registry keys

Monitoring and control capabilities

A key feature of CBRegistry is its ability to intercept requests before they reach the registry, allowing the application to modify or handle the request in advance. Alternatively, the application can be notified after the registry processes the request, giving it the option to understand the outcome of the operation and potentially alter it before the result is returned to the originating process.

CBRegistry enhances performance by letting you set rules that define which types of requests should be reported, when they should be reported (before or after reaching the registry), and which specific registry keys to monitor. These conditions can include not just key names or paths, but also specific processes to track.

With each request, the application can identify who initiated it (the user) and which process was involved, enabling the implementation of behavior tailored to specific processes and users. This behavior can be controlled dynamically through event handlers rather than through static rules.

The application can modify parameters or associated data, complete the request with an error, or override an error to report success. If the event is reported before reaching the registry, the application can fulfill or deny the request without passing it to other filters or the registry itself.

Performance Considerations

Since the driver receives all requests sent to the registry, improper configuration can negatively affect performance. CBRegistry offers several methods to help minimize this impact.

First, applications can establish fine-grained rules to prevent excessive notifications. Additionally, access rules can be configured to enforce registry access control without requiring communication back to user mode.

Furthermore, you can define pass-through rules to specify which requests should be ignored, even if they match existing filter rules.

Finally, many events come with parameters that allow handlers to skip processing further requests related to the same key until it is closed.

Access and Default Rules

Events are useful for dynamically handling requests, but they do consume extra system resources and can slow down registry operations. Additionally, they require your application to be running to function properly. For scenarios involving registry protection, the CBRegistry driver includes two special types of rules: Access rules and Default rules (which are discussed in more detail in a dedicated article).

Access rules instruct the driver to allow or deny specific operations directed at certain registry keys. These rules are similar to standard filter rules in that they remain active while the application is running. However, they don't require the driver to switch back to user mode for processing.

Default rules serve the same purpose as Access rules, but they remain effective even when the application that set them is not running.

Best Practices and Tips

The most common pitfalls to avoid are:

• Capturing too many events for too many keys: While it may be tempting to set a filter rule to capture all events across every registry key, doing so can significantly impact performance. Instead, focus on creating fine-tuned rules that target a specific subset of keys or trigger events only for particular types of requests.
• Adding too many rules: Although this advice might seem contradictory to the previous point, it's important to recognize that rules come with their own costs. While adding a few rules is generally fine, introducing a hundred or more can lead to increased CPU usage during processing. Finding the right balance between the number of rules and the frequency of callbacks to user mode requires testing your application in real-world scenarios.
• Trying to do too much in event handlers: If your application needs to perform complex actions in response to a registry request, consider offloading these tasks to a separate worker thread for asynchronous execution. This approach not only enhances system stability but also helps prevent unexpected interactions with third-party software.

Getting Started with CBRegistry

You can find an evaluation version of the SDK for your platform and programming language in the Download Center. After downloading and installing the SDK, you will receive a library, sample code, and comprehensive documentation on your system. The documentation includes a "Getting Started" section with programming instructions. Additionally, free technical support is available during the evaluation phase.