Which of the following is the first step to secure a newly deployed server?

Closing unnecessary service ports is the critical first step because it immediately reduces the attack surface of the newly deployed server. By disabling or blocking ports not required for the server's intended function, you prevent potential attackers from exploiting vulnerabilities associated with those services. While updating software, adding to an ACL, and upgrading the OS are all important security measures, they typically occur after the initial hardening of the server's immediate exposure. Updating software (patches) addresses known vulnerabilities, but an open, unneeded port still presents a risk. Adding to an ACL controls network access, but the server itself should first be hardened. Upgrading the OS is a significant change that usually follows initial deployment and hardening.