Which of the following is a prerequisite for privilege escalation to occur?

Which of the following is a prerequisite for privilege escalation to occur?

A.
The attacker has to create their own zero day attack for privilege escalation.

B.
The attacker must already have physical access to the system.

C.
The attacker must use a rootkit in conjunction with privilege escalation.

D.
The attacker must have already gained entry into the system.