Which guidance document serves as an audit guide?

The document that serves as an audit guide is 800-53A. This publication is specifically designed to provide guidance on assessing security and privacy controls within federal information systems and organizations. It expands on the NIST SP 800-53 framework, which outlines recommendations for security controls, while 800-53A focuses on the assessment processes for those controls.

By detailing how to conduct assessments and evaluate compliance, 800-53A serves as a practical tool for auditors to effectively measure the implementation and effectiveness of the security measures in place. This means it includes methodologies, strategies, and expected outcomes for the audit process, ensuring that organizations can have a consistent and thorough approach to evaluating their security posture.

In contrast, documents such as 800-53 outline the controls themselves, 800-30 focuses on risk management and risk assessment, and 800-39 deals with the overall risk management framework - none of which specifically cater to the assessment or auditing process as clearly as 800-53A does.