Oracle Linux 6 no longer boots in virtual box after update

After running yum update on my Oracle Linux 6.7 the system no longer boots into runlevel 5. The last message on the boot screen is
Starting atd: [ OK ]
but the system does not boot into graphical environment anymore.

I can boot into runlevel 3 by

• pressing any key at the boot prompt to enter the boot menu
• press the "e" key on the line of the kernel I want to boot
• use the cursor keys to move to the line which starts with "kernel /vmlinuz [...]"
• again press the "e" key on that "kernel" line 
• append " 3" at the end of the line and press ENTER
• and press the "b" key to boot with that modifications 

Now the system comes up. Looking into the /var/log directory, I see a couple of Xorg.<n>.log files.

One of those files shows the following error message:

(II) LoadModule: "vboxvideo"

(II) Loading /usr/lib64/xorg/modules/drivers/vboxvideo_drv.so

(II) Module vboxvideo: vendor="Oracle Corporation"

    compiled for 1.10.0, module version = 1.0.1

    Module class: X.Org Video Driver

    ABI class: X.Org Video Driver, version 10.0

(EE) module ABI major version (10) doesn't match the server's version (15)

(II) UnloadModule: "vboxvideo"

(II) Unloading vboxvideo

(EE) Failed to load module "vboxvideo" (module requirement mismatch, 0)

(EE) No drivers available.

(EE)

Fatal server error:

(EE) no screens found(EE)

The cause of this error is that the upgrade of the Linux OS does not re-configure the vbox additions (see https://www.virtualbox.org/ticket/13522)

So I need to run

/etc/init.d/vboxadd-x11 setup 

as root. A new reboot now boots into graphical mode again.

Another solution is to rename (or delete) /etc/X11/xorg.conf.

But the VBox Guest Addition is still not working (which it did before the upgrade). For this, the VBOXADDITIONS setup has to be run again.