Which of the following should be determined FIRST when a new security vulnerability is made...

The very first action in vulnerability management is confirming whether the affected technology exists in the organization’s environment.

CRISC notes:

“Before prioritizing or mitigating, it is critical to determine whether the enterprise uses the affected asset or service.”

If the organization is not using the affected technology, no further response is required.

After that, severity and mitigating controls are reviewed.

Hence, C is correct.

CRISC Reference: Domain 2 – IT Risk Assessment, Topic: Vulnerability and Asset Validation.