Assess CUI safeguards with evidence, depth, and coverage chosen up front

Bottom line: an assessment result is only interpretable when its boundary, evidence, methods, sample, depth, coverage, assessor role, and date are clear. A control narrative or screenshot can support a conclusion, but neither automatically proves that the safeguard is designed correctly and operating across the full CUI environment.

Source fact: what NIST SP 800-171A provides

NIST SP 800-171A Revision 3 provides assessment procedures and a methodology for evaluating the security requirements in SP 800-171. NIST states that the procedures are flexible and can be customized to organizational and assessor needs. Assessments may be independent, third-party, or government-sponsored and can use varying degrees of rigor through customer-defined depth and coverage attributes.

This flexibility makes planning visible: two assessments of the same requirement may not provide the same assurance if their scope, depth, coverage, evidence, or independence differs.

What the source does not establish

SP 800-171A does not determine the applicable contract, define the CUI boundary, accredit every assessor, or by itself establish a particular certification outcome. Completing a worksheet does not prove that evidence is authentic, representative, current, or sufficient.

This draft does not interpret contractual scoring, certification, or regulatory rules. Those must be confirmed from the governing authority and current program documentation. Sensitive assessment artifacts can themselves reveal security information and require controlled handling.

Applicability questions

What agreement, requirement set, system boundary, and assessment objective are authoritative?

Who is the customer for the assessment, and what independence or qualification is required?

Which examination, interview, and test methods will be used for each objective?

What depth and coverage are necessary for the risk and required conclusion?

How will samples represent sites, systems, roles, shifts, components, and time periods?

DSE recommendation: plan before collecting artifacts

The following steps are DSE recommendations based on the cited source.

Freeze the assessment basis: applicable SP 800-171 revision, authorized boundary, requirements, organizational components, shared services, suppliers, dates, and exclusions.

Define assessor roles, independence, access, evidence handling, conflict resolution, and reporting authority. Confirm any external program requirements separately.

Tailor procedures intentionally. Record the selected methods, depth, coverage, samples, and rationale for every requirement or assessment objective.

Seek multiple evidence types where warranted. Compare documented design, responsible-person explanation, configuration or record examination, and observed or tested operation.

Time-bind conclusions. Note evidence dates, versions, environments, exceptions, temporary states, and changes occurring during the assessment.

Track findings to root condition, owner, planned action, due date, residual risk decision, retest, and verified closure. Do not erase the original finding when remediation occurs.

Verification and evidence

Retain the approved assessment plan, boundary and requirement baseline, evidence request list, chain-of-custody or access controls where needed, interview and test records, samples, assessor work papers, findings, management responses, retest results, and final report. A reviewer should be able to reconstruct how each conclusion was reached.

Official references

NIST SP 800-171A Rev. 3 — Assessing Security Requirements for Controlled Unclassified Information — National Institute of Standards and Technology; published May 2024

NIST SP 800-171 Rev. 3 — Protecting CUI in Nonfederal Systems and Organizations — National Institute of Standards and Technology