Comment # 4 on bug 1204435 from Larry Rainey

Here is a script to install the extension pack (only on the host - it not to be
loaded on the guests). It adds the hooks to the resize, clipboard and files to
allow a guest with guest additions to talk to the host.

Guest additions on Linux should come from the Linux version - they are kernel
dependent and Oracle Virtualbox CD does not always work correctly.

All Non-Linux guest should use the Oracle CD to install the guest additions.

Without VirtualBox running on the host create a file with these lines

#/usr/bin/bash
echo update VirtualBox Extension Pack
VBOX_VERSION=`/usr/bin/VBoxManage --version | awk -F_ {'print $1'}`
VBOX_EXT_VERSION=`/usr/bin/VBoxManage --version | awk -F_ {'print $1'}`
# echo Virtualbox version installed is $VBOX_VERSION and $VBOX_EXT_VERSION
VBOX_EXT=`echo
Oracle_VM_VirtualBox_Extension_Pack-${VBOX_EXT_VERSION}.vbox-extpack`
# echo File is $VBOX_EXT
cd /tmp
/usr/bin/wget http://download.virtualbox.org/virtualbox/$VBOX_VERSION/$VBOX_EXT
echo y | /usr/bin/VBoxManage extpack install --replace $VBOX_EXT
rm -f $VBOX_EXT

I call mine addvbext.sh 

sudo bash addvbext.sh