Little Snitch 4 needs to install a Network Kernel Extension in order to perform its network traffic filtering. This kind of kernel extension is no longer supported on macOS Big Sur. The operating system now refuses to load such kernel extensions by default.
The latest version 5 of Little Snitch no longer uses this unsupported Kernel API. It uses the newer System Extension API provided by Apple and is therefore fully compatible with macOS Big Sur.
Alternatively, it’s currently still possible to manually approve the loading of particular kernel extensions. This requires to start up your computer from macOS Recovery and enter a Terminal command to grant the necessary permission. However, Apple may remove this possibility at any time with a future update of macOS Big Sur.
Start up your computer from macOS Recovery: Restart your computer and hold Command-R during startup.
Open the Terminal application from the Utilities menu in the menu bar.
Enter the following command and press Return:
spctl kext-consent add MLZF7K7B5R
Restart your computer by choosing Restart from the Apple menu ().
- Uninstall Little Snitch 5 if it’s already installed on your computer.
After this approval process you should be able to install Little Snitch 4.6.
Important Note: Older versions of Little Snitch (prior to version 4.6) cannot be installed on macOS Big Sur, not even with this manual approval.