Identifying the number of security flaws within the system is the best assessment metric to understand a system’s vulnerability to potential exploits. A security flaw is a weakness or a defect in the system’s design, implementation, or operation that could be exploited by an attacker to compromise the system’s confidentiality, integrity, or availability2. By identifying the number of security flaws within the system, the assessor can measure the system’s vulnerability, which is the degree to which the system is susceptible or exposed to attacks3. Determining the probability that the system functions safely during any time period, quantifying the system’s available services, and measuring the system’s integrity in the presence of failure are not assessment metrics that directly relate to the system’s vulnerability to potential exploits, as they are more concerned with the system’s reliability, availability, and resilience. References: 2: CISSP For Dummies, 7th Edition, Chapter 8, page 2173: Official (ISC)2 CISSP CBK Reference, 5th Edition, Chapter 8, page 461.