Dropbox filesystem integration: an overview

The kernel extension for MacOS is currently in closed beta for select opt-in users only. The minifilter driver for Windows will be introduced in a future version of the desktop client later this year.

The Dropbox desktop client uses lightweight integrations with the Windows and MacOS operating systems to function. These integrations are called drivers (on Windows) and kernel extensions (on MacOS), and they allow Dropbox to receive notice of file and folder actions and sync them.

How it works

Use of the kernel extensions and minifilter drivers is common among many popular systems:

  • Hardware—like your computer’s hard drive, printers, and copiers
  • Filesystems—like those exposed through Server Message Block (SMB)
  • Software—like antivirus or virtualization programs

Select your operating system to learn more about kernel extension or minifilter driver on your specific computer.

Macintosh

On MacOS, Dropbox uses a kernel extension. This extension gives Dropbox low-level access to your computer’s file system, and allows the app to run more smoothly.

Vista/Win7/Win8/Win10

On Windows, the Dropbox desktop client uses minifilter driver. This driver enables a better integration between Dropbox and your filesystem. For example, this integration allows Dropbox to receive information about changes to your files and sync them to your Dropbox account.

Permissions

Dropbox used publicly-available APIs from Apple and Microsoft to write the kernel extension and minifilter driver. No additional admin permissions are required (beyond what Dropbox has always needed to function).

What kernel extensions actually do

Kernel extensions enable "callbacks." Callbacks are real-time calls that confirm you have permission to do things like move, delete, or change ownership of content in shared spaces. If you don’t have these file access permissions, kernel extensions allow Dropbox to send warnings when you may be taking an action that could unshare folders or delete shared content.

Security and usage

Kernel extensions and minifilter drivers can give applications additional access to your computer’s operating system. Dropbox is cautious in only using these extensions to improve your experience with our app.

Some notes on what we do not do:

  • We do not use kernel extensions to interact with any files other than those stored in your Dropbox
  • We do not use kernel extensions to make network requests
  • We do not use kernel extensions to parse any data in the kernel
  • We do not use kernel extensions to read or write files

Security and stability

Dropbox takes great measures to protect your data and privacy, and we designed the minifilter driver and kernel extension with security and stability as top priorities. In fact, many of the engineers who wrote this extension previously worked on filesystem technologies at various OS vendors.

These components have gone through extensive security reviews with internal security teams, as well as audits done by external penetration testers. We’ve run these components both internally at Dropbox and in cooperation with enterprise-scale beta customers. In both cases these components ran successfully.

Alternatives

These integrations are core to current and future Dropbox client services. There is no way to disable or opt-out of using the minifilter driver or kernel extension on the Dropbox desktop client. Doing so would also disable important alerts that prevent users from accidentally deleting shared data, or taking unintended file actions.

If you don’t want to install the Dropbox desktop application, you can view, share, and download your files without the desktop integration by using only the Dropbox website at dropbox.com.

Read the blog post about the technical background of the Dropbox kernel extension.

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