An Ubuntu operating system release is considered 'supported' if the vendor continues to provide security patches for the product. With an unsupported release, it will not be possible to resolve security issues discovered in the system software.
Upgrade to a supported version of the Ubuntu operating system.
The following resource is also helpful.
This security hardening control applies to the following category of controls within NIST 800-53: System and Information Integrity.This control applies to the following type of system Unix.