It is certainly not typical for CNC Controls or Industrial Automation Systems to be accessible to exploit without a network first being compromised, but the ramifications can be very significant. For that reason we keep an eye on the security updates related to Industrial Automation Systems. If you do not have any of these systems in your facility this can still serve as a reminder to keep your critical systems isolated from your regular user networks to avoid the potential of this sort of vulnerability being used to adversely affect your operations.
If you are utilizing these systems we urge you to read the Siemens bulletin and consider upgrading to release V4.0.0 which according to SIEMENS fixes these vulnerabilities:
Siemens provides the SIMATIC S7-1200 CPU product release V4.0.0  which fixes these
As a general security measure Siemens strongly recommends to protect network access to
S7-1200 CPUs with appropriate mechanisms. It is advised to follow recommended security
practices  and to configure the environment according to operational guidelines  in order
to run the devices in a protected IT environment.
Here is an image of the US-CERT Advisory related to this:
Any computer system connected to your CNC Controls and Industrial Automation Systems should be well protected to ensure that it is not used to compromise your mission critical equipment. Most IT departments are very aware of this and plan accordingly, please consider this development as a reminder of the importance of protecting these assets that are so critical to your business.