"unknown X server version"Apart of the updated Virtualbox version this guide also assumes functional Fedora Linux installation with working Internet connection. Lastly, the aim here is to provide a generic guide for Virtualbox Guest additions on Fedora Linux virtual machine and as a result reader needs to adjust some of the following linux commands to is your envireoment.
Step 1: Mount Guest additions
Start your Fedora virtual machine and mount Virtualbox Guest additions by navigating toVirtual box menu -> Devices -> Insert Guest Additions CD image
The following message will pop up: 
Hit cancel and navigate to Virtualbox Guest additions mounted directory using your terminal:
# mount | grep -i vbox /dev/sr0 on /run/media/fedora/VBOXADDITIONS_VERSION type iso9660 # cd /run/media/fedora/VBOXADDITIONS_VERSION # ls 32Bit AUTORUN.INF cert runasroot.sh VBoxSolarisAdditions.pkg VBoxWindowsAdditions.exe 64Bit autorun.sh OS2 VBoxLinuxAdditions.run VBoxWindowsAdditions-amd64.exe VBoxWindowsAdditions-x86.exe
Step 2: Install pre-requisites
Now that we have our guest additions we need to install development tools which a prerequisites for successful Virtualbox Guest additions modules compilation. There is one thing to keep in mind when before the running the following linux command. The Virtualbox Guest additions modules compilation will be done against your currently running kernel. This simply means that with every kernel update you will need to install appropriate version of kernel headers and recompile Virtualbox Guest additions modules.yum install kernel-devel-$(uname -r) kernel-headers-$(uname -r) gcc
Step 3: Install and compile Virtualbox Guest additions
At this stage we are ready to install Virtualbox Guest additions. Still in the Virtualbox Guest additions directory executeVBoxLinuxAdditions.run
script: # ./VBoxLinuxAdditions.run Verifying archive integrity... All good. Uncompressing VirtualBox 4.3.12 Guest Additions for Linux............ VirtualBox Guest Additions installer Removing installed version 4.3.12 of VirtualBox Guest Additions... Copying additional installer modules ... Installing additional modules ... Building the VirtualBox Guest Additions kernel modules Building the main Guest Additions module [ OK ] Building the shared folder support module [ OK ] Building the OpenGL support module [ OK ] Doing non-kernel setup of the Guest Additions [ OK ] Starting the VirtualBox Guest Additions [ OK ] Installing the Window System drivers Installing X.Org Server 1.14 modules [ OK ] Setting up the Window System to use the Guest Additions [ OK ] You may need to restart the hal service and the Window System (or just restart the guest system) to enable the Guest Additions. Installing graphics libraries and desktop services component[ OK ]All is now ready to reboot your system for VirtualBox Guest Additions to take effect. If you installation fails from some reason make sure to read
/var/log/vboxadd-install.log
for additional information the help you resolve your problem.