What Is CBFS Filter and How Does It Intercept Filesystem Operations?

Updated

CBFS Filter is a developer SDK component from Callback Technologies that intercepts, monitors, and controls filesystem, registry, and process operations in real time. You use it when an application must enforce filesystem-level access control or security policies — for example, blocking writes to protected folders, logging who opens which files, or redirecting an operation before it completes. It is aimed at Windows-style production software where the alternative would be writing a kernel-mode driver yourself; the component supplies the driver layer and exposes an application-level API, so your code works at the API level rather than in kernel mode.

How the interception works

The mechanism is a filter placed in the operating system's I/O path. Every filesystem, registry, or process operation passes through this filter before it reaches its target, and the filter calls back into your application. Your handler then decides what happens next:

  • Allow — the operation proceeds unchanged.
  • Block — the operation is denied and the caller receives an error.
  • Modify — the operation is altered before it completes (for example, changing a path or the data being written).

Because the decision happens in real time, before the operation finishes, the policy is enforced at the system level rather than after the fact. A concrete case: a compliance tool that must prevent any process except an approved backup agent from reading a set of files. The filter sees each open request, checks the requesting process identity, allows the backup agent, and returns access-denied to everything else — without the tool needing its own kernel driver.

What you build with it

The page positions CBFS Filter around "enforce filesystem-level access control and security policies by intercepting filesystem, registry, and process operations in real time." Typical applications:

  • Access control and security policy enforcement — allow/deny rules tied to users, processes, or paths.
  • Monitoring and auditing — capture a record of file, registry, and process activity.
  • Real-time control — intervene in an operation while it is in flight, not just observe it afterward.

The SDK ships with APIs, drivers, documentation, and samples, per the product description, and the same API family is described as consistent across the vendor's components.

How it differs from neighboring components

CBFS Filter is one of several components, and choosing the right one depends on what you need to do:

Component What it does Choose it when
CBFS Filter Intercepts and controls filesystem, registry, and process operations in real time You need to allow, block, or modify operations and enforce policy
CBFS Connect Presents any data source (cloud storage, databases, REST APIs, custom content) as local files and folders You need to create a virtual filesystem, not police an existing one
CBFS Encrypt Transparently encrypts files; authorized processes decrypt on the fly, others see ciphertext You need file-level encryption policy rather than operation interception
CBFS Sync Bidirectional sync between local and remote storage with placeholder files and on-demand hydration You need synchronization, not access control

The distinction matters: CBFS Connect and CBFS Filter are often confused because both touch the filesystem layer, but Connect supplies content while Filter governs operations on content that already exists. If your goal is encryption specifically, CBFS Encrypt is the narrower fit; Filter is the general-purpose interception layer.

What to check before committing

  • Platform fit. The product is described in Windows-oriented terms (filesystem, registry, and process operations). Confirm the target OS support in the current documentation before designing around it.
  • Driver installation. Even though you avoid writing kernel code, a driver is still installed as part of deployment; plan for installation and signing requirements in your release process.
  • Evaluation. The site advertises a free trial and subscription licensing, so you can prototype against real workloads before purchase. Pricing details are not published on the page, so confirm terms with the vendor.
  • Scope of interception. Decide up front whether you need filesystem operations only or also registry and process events, since that shapes your handler design and performance testing.

If your requirement is to watch and control what happens to files in real time, CBFS Filter is the direct fit; if you instead need to expose data as a drive or encrypt files transparently, start with CBFS Connect or CBFS Encrypt.