CBFS® Filter

Monitor and Control File and Folder Operations in Your Windows Applications


Use CBFS Filter to track any low-level file system events and react to them on-the-fly. Your user-mode application receives notifications (callbacks) when file operations are executed. In addition to simple notifications, your application can modify data, encrypt files, deny access, or even cancel the request.

Implement Continuous Data Protection (CDP)

Control access to files on the file system level. Encrypt and decrypt files on-the-fly. Assign specific permission schemas. All file system calls can be analyzed and treated before passing them to the underlying file system.

Secure Individual Files and Regulate Access to Them

Secure individual files by encrypting and decrypting them on-the-fly. Control which applications may read the decrypted files and when. Industry-standard strong encryption algorithms are supported.

Audit Application Access to Files

Control any action of file-accessing applications. Intercept any file system call, analyze its content, log it, modify, permit its execution, or cancel it altogether. This control may be based on any file parameters.

Proactively Intercept and Modify File Access Requests

Proactively implement rule-based request interception. CBFS Filter can intercept a request, analyze it, and modify or log its parameters before the file system executes it.

Create Virtual Files and Directories

Create virtual files and directories on existing disks. Such files and directories are recognized by Windows and other applications as real files.

Replace The Ineffective FileSystemWatcher Class

With CBFS Filter, you will not miss a single file system event and will get all event details. You can even modify or prevent the file system operation if needed.

CBFS Filter is a software development kit for Windows applications that tracks any file requests on-the-fly. Your user-mode application gets notification (callback) when a file operation is executed. In addition to simple notifications, CBFS Filter lets your application decide how to process a request: whether modify input or output data before or after the request is performed or even cancel the request.

  • Synchronous callbacks on all main filesystem requests (file create/open, read/write, seek, get information, close, delete, rename, enumerate directories)
  • Asynchronous notifications on all main filesystem requests
  • Per-process filtering of file and directory access (possibility to allow or forbid access based on process and owner information)
  • Synchronous callbacks on path reparsing (these callbacks let you change path to the file being accessed thus redirecting the request)
  • Creation of virtual files and directories on existing filesystems
  • Possibility to setup access rules that will be used during system boot (i.e. when the application is not running)
  • Access, default, passthrough, and reparse rules

The CBFS Filter driver intercepts various requests going to the file system. If the request matches one of the rules, specified by the application, the driver performs the action defined by the rule. The action can be to process or decline the request unconditionally and to call the callback function in your application synchronously or asynchronously. Your callback can also decline or allow the request, perform the request itself (not passing it further), or post-process the request.

The user-mode API is simple and introduces functions specific to driver management and storage mounting operations. Also, the API includes callback functions (events) which your application can handle to receive notifications about different types of file system requests.


  • Windows Vista, 7, 8, 8.1, 10
  • Windows Server 2008, 2008 R2, 2012, 2012 R2, 2016

Microsoft .NET Framework

  • 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.6, 4.7.x


  • Visual Studio 2008, 2010, 2012, 2013, 2015, 2017


  • Visual Studio 2008, 2010, 2012, 2013, 2015, 2017

VCL API (no need for external DLLs)

  • Delphi 2007 to Delphi 10.2 Tokyo (32-bit Windows Only)
  • C++ Builder XE to C++ Builder 10.2 Tokyo (32-bit Windows Only)
In addition to CBFS Filter, Callback Technologies also offers several other virtual storage products. These products have many features in common, however, they are designed for various tasks and can be integrated with one another to fit your needs. If you are unsure what product(s) to choose, please read the comparison here.

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Download Now v2017.0.5 | 01/30/2018

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