Information
The /var/tmp directory is a world-writable directory used for temporary storage by all users and some applications. Since the /var/tmp directory is intended to be world-writable, there is a risk of resource exhaustion if it is not bound to a separate partition. In addition, making /var/tmp its own file system allows an administrator to set the noexec option on the mount, making /var/tmp useless for an attacker to install executable code. It would also prevent an attacker from establishing a hardlink to a system setuid program and wait for it to be updated. Once the program was updated, the hardlink would be broken and the attacker would have his own copy of the program. If the program happened to have a security vulnerability, the attacker could continue to exploit the known flaw.
Solution
For new installations, during installation create a custom partition setup and specify a separate partition for /var/tmp For systems that were previously installed, create a new partition and configure /etc/fstab as appropriate.