1. Add source
# sudo vim /etc/apt/sources.list
...
...
...
### VirtualBox5.2.x.
deb http://download.virtualbox.org/virtualbox/debian bionic contrib
...
...
...
!wq
2. Add Keys
# wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add -
# wget -q https://www.virtualbox.org/download/oracle_vbox.asc -O- | sudo apt-key add -
3. Install
# sudo apt-get update
# sudo apt-get install virtualbox-5.2