You work for an enterprise that provides various cybersecurity services. You are assigned to examine an enterprise's network and suggest security measures modifications, if necessary. On examining the network, you find that the enterprise hosts most of its computing resources on a cloud platform and few resources on$-$premises, and both seem to have secure settings implemented. You also find that the enterprise computers use the Windows XP operating system.

Which of the following vulnerabilities should you insist on fixing first?

a$.$ Configuration vulnerability

b$.$ Zero$-$day vulnerability

c$.$ Third$-$party vulnerability

d$.$ Platform vulnerability