Thank you Socratis, but I am a bit perplexed by your note, particularly by your language.
I am sorry, but I need to correct you.
Thank you Maxeed for the post, but that's where the links to the Apple website point to. And you do not have to do a manual load of the kernel or anything like that. Simply re-installing VirtualBox will trigger that security warning in the System Preferences. It's already been told in previous posts, as well as in the links that we've been sending people to.
But this security problem that is easily solvable; re-install VirtualBox.
Thank you, but it took me a while to figure out the issue using Google. My understanding is that High Sierra enforces manual kext approval.
This is something new, and I didn't know that. Virtualbox was working after the upgrade to HS, but I decided to format my Mac and reinstall a clean copy of MacOS, that's where the problem started.
However, it is not just a reinstall. You need to install, approve, reinstall, approve, etc, until all the extensions are approved.
The "kernel is not loading" error was there before 10.13 (since 2012 if you follow the other link) and the logs point to something failing in the postflight script.
VirtualBox kernel extensions not loading is a problem that may occur during installation, it has been there since there's a Virtualbox for Mac, for many different reasons.
The logs are not pointing to "something falling" in the posflight script. They tell exactly what is falling.
In this specific case, a change in the High Sierra security policies now requires the manual approval of every new kernel extensions.
The technical part could end here but...
it usually has to do with systems that they've been manually altered. The manual tinkering with kexts is hocus pocus, and quite frankly a seriously dangerous advice.
Loading a kernel extension manually is not tinkering, and it is far from magical hocus pocus.
I was simply trying to understand why the extension was not loaded, and sharing the output of the command here will help other people in a similar situation when they google the actual error.
If you want to screw your system, you're free, but VirtualBox has serious security measures in place to not let you work with it after that. So, with a screwed system, no more VirtualBox. Simple...
WOW, so, let me get this straight:
Screwing my system (literally?) is free. But Virtualbox has "serious security", very puritan "no-screwing under my hood" measures in place. It is beyond my imagination how this could even be remotely possible.
A proper translation of your sentence is:
Virtualbox has a complex integration with MacOS, and custom low level modification of the OS may prevent its kernel extensions to properly load, making VirtualBox unable to function properly.
Thank you, but this is not my case.