VirtualBox 5.2 Won't Install on Mac OS 10.13
This worked for me on High Sierra 10.13.4:


System Preferences > Keyboard > Shortcuts > Select 'All Controls'




Then:


System Preferences > Privacy &amp; Security > Press 'Tab' until 'Allow' is selected > Press 'Spacebar'


Note: the Privacy &amp; Security page may need to be unlocked before 'Tab' will work.

Hope this helps!

Credit to @dansanduleac's answer on GitHub