TheCMMC Assessment Guideis the best source for determining the sources of evidence for a given practice because it provides specific guidance on how organizations should implement and demonstrate compliance with CMMC practices. Each CMMC level has its own assessment guide (e.g.,CMMC Assessment Guide – Level 1, Level 2), detailing expected evidence and assessment procedures.

Detailed Justification:

CMMC Assessment Guide (Primary Source for Evidence)

TheCMMC Assessment Guideexplicitly outlines the evidence required to verify compliance with each practice.

It provides detailed instructions on assessment objectives, clarifying what assessors should look for when determining compliance.

The guide breaks down each practice intoassessment objectives, helping organizations prepare appropriate documentation and artifacts.

Other Documents and Why They Are Not the Best Choice:

NIST SP 800-53 (Option A)

WhileNIST SP 800-53provides a comprehensive catalog of security and privacy controls, it does not focus on CMMC-specific evidence requirements.

It serves as a foundational cybersecurity framework but does not define the specific artifacts required for CMMC assessment.

NIST SP 800-53A (Option B)

NIST SP 800-53Aprovides guidance on assessing security controls but is not tailored to the CMMC framework.

It includes general control assessment procedures, but theCMMC Assessment Guideis more precise in defining the evidence needed for CMMC compliance.

CMMC Assessment Scope (Option C)

TheCMMC Assessment Scopedocument outlines which systems, assets, and processes are subject to assessment.

While important for defining boundaries, it does not provide details on specific evidence requirements for each practice.

References from Official CMMC Documents:

CMMC Assessment Guide (Level 2) – Section on "Assessment Objectives"

This document details how evidence is collected and evaluated for each CMMC practice.

Example: ForAC.L2-3.1.1 (Access Control – Limit System Access), the guide specifies that assessors should verify documented policies, system configurations, and audit logs.

CMMC Model Overview (Official DoD Documents)

Emphasizes thatCMMC Assessment Guidesare the official reference for determining sources of evidence.

Conclusion:

TheCMMC Assessment Guideis the most authoritative source for determining the required evidence for a given practice in CMMC assessments. It provides detailed breakdowns of assessment objectives, required artifacts, and verification steps necessary for compliance.