VirtualBox 4.3.18 is packaged with Debian 8 and Debian 7 backports. Debian 7 stable is packaged with VirtualBox 4.1.18, it's Guest Additions to not build on kernel 3.16 which is the latest kernel on Debian 8.5. To fix, you need to upgrade VirtualBox to 4.3.18. See Ticket #13123
Follow VirtualBox on the Debian Wiki:
# Backported packages for Debian 7 "Wheezy" deb http://http.debian.net/debian/ wheezy-backports main contrib
# apt-get update
# apt-get install linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,')
# apt-get -t wheezy-backports install virtualbox
This will also install wheezy-backports/virtualbox-dkms and other recommended packages. DKMS will build the VirtualBox modules for your system.
Check whether the Guest Additions have installed to 4.3.18, if not, then you must install the 4.3.18 Guest Additions manually:
dpkg -i <downloaded-package>
Follow these steps to install the Guest Additions on your Debian virtual machine:
If the header files are not found, or the wrong header files are found, do the following:
sudo apt-get remove dkms build-essential linux-headers-* sudo apt-get install dkms build-essential linux-headers-$(uname -r)
enable backports with contrib; to do so, add a line like
deb http://ftp.debian.org/debian stretch-backports main contrib
to /etc/apt/sources.list (or better yet, a stretch-backports.list file in /etc/apt/sources.list.d);
install virtualbox-guest-dkms, kernel headers, and, optionally, virtualbox-guest-x11 (for the graphical guest utilities):
sudo apt update sudo apt install virtualbox-guest-dkms virtualbox-guest-x11 linux-headers-$(uname -r)