What is Ryan's best option to verify that no unnecessary ports and services are available on his systems without using a vulnerability scanner?

Conducting a configuration review is the best option for Ryan to verify that no unnecessary ports and services are available on his systems. A configuration review involves systematically analyzing system settings, services, and active configurations to ensure they align with security policies and best practices. This review allows Ryan to identify any extraneous services or open ports that should be disabled to minimize potential attack surfaces and enhance security.

By scrutinizing the configurations on the systems, Ryan can directly assess which services are running and check their necessity for business functions. This proactive approach helps ensure that only required services are active, thereby strengthening the overall security posture of the systems.

Other options, while relevant to security, do not specifically address the need to verify configurations related to ports and services. For example, running a malware scan focuses on identifying malicious software rather than examining system configurations. Implementing network segmentation is a strategic approach to network security but doesn't directly verify ports and services on individual systems. Disabling firewalls would actually create security risks rather than helping with the verification process. Thus, conducting a configuration review stands out as the most effective means for Ryan to achieve his goal.