/lib/udev/rules.d/60-virtualbox-guest-dkms.rules is in virtualbox-guest-dkms 4.1.42-dfsg-1+deb7u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | KERNEL=="vboxguest", NAME="vboxguest", OWNER="root", MODE="0660"
KERNEL=="vboxuser", NAME="vboxuser", OWNER="root", MODE="0666"
|