For virtualbox you should install DKMS package:
sudo apt-get install dkms
You should not pin kernel versions as they contain security and stability fixes! Meltdown & Spectre as examples.
Continue only if you are completely sure what you are doing.
For kernel packages pinning see my other answer.
If you understand what you are going to achieve (with lowering security, of course) - you should pin the following packages:
To make Synaptic and APT pins consistent (see my other answer):
sudo ln -s /etc/apt/preferences.d/synaptic /var/lib/synaptic/preferences