Ideally, the vagrant box image used by dcos-vagrant includes VirtualBox Guest Additions compatible with the latest versions of VirtualBox. It should "just work".
However, if they are out of date or incompatible with your installed version of VirtualBox you may want to install the VBGuest Vagrant Plugin to automatically install VirtualBox Guest Additions appropriate to your local VirtualBox version on each new VM after it is created.
vagrant plugin install vagrant-vbguestThis allows the pre-built vagrant box image to work on multiple (past and future) versions of VirtualBox.