정답: A
An audit report of the controls by the service provider's external auditor provides the best evidence that a third-party service provider's information security controls are effective. An external auditor is an independent and objective party that can assess the design and operating effectiveness of the service provider' s information security controls based on established standards and criteria. An external auditor can also provide an opinion on the adequacy and compliance of the service provider's information security controls, as well as recommendations for improvement.
Documentation of the service provider's security configuration controls is a source of evidence that a third- party service provider's information security controls are effective, but it is not the best evidence.
Documentation of the security configuration controls can show the settings and parameters of the service provider's information systems and networks, but it may not reflect the actual implementation and operation of the controls. Documentation of the security configuration controls may also be outdated, incomplete, or in accurate.
An interview with the service provider's information security officer is a source of evidence that a third-party service provider's information security controls are effective, but it is not the best evidence. An interview with the information security officer can provide insights into the service provider's information security strategy, policies, and procedures, but it may not verify the actual performance and compliance of the information security controls. An interview with the information security officer may also be biased, subjective, or misleading.
A review of the service provider's policies and procedures is a source of evidence that a third-party service provider's information security controls are effective, but it is not the best evidence. A review of the policies and procedures can show the service provider's information security objectives, requirements, and guidelines, but it may not demonstrate the actual execution and enforcement of the information security controls. A review of the policies and procedures may also be insufficient, inconsistent, or outdated.
References:
* ISACA, CISA Review Manual, 27th Edition, 2019, p. 284
* ISACA, CISA Review Questions, Answers & Explanations Database - 12 Month Subscription
