03.16.03OFFICIAL TITLEPENDING NIST SME REVIEW

03.16.03 — External System Services

03.16 System and Services Acquisition · NIST SP 800-171 Rev. 3

Independent summary of the official requirement

Require the providers of external system services used to process, store, or transmit CUI to conform to the organization's security requirements, and define and document organizational oversight and the user roles and responsibilities associated with those services.

Rev. 3 requirement text is multi-part and parameterized with organization-defined values, so this site summarizes rather than reproduces it. The summary is independent — read the official publication for the binding wording.

NIST SP 800-171 Rev. 3 — Protecting CUI in Nonfederal Systems ↗NIST SP 800-171A Rev. 3 — Assessing Security Requirements for CUI ↗

Independent interpretation

What this requirement is after

When CUI runs through someone else's service, the organization still owns the outcome. This requirement makes the arrangement explicit: security requirements imposed on the provider, a named person inside the organization watching the service, and clarity about what users may do with it — because 'the cloud provider handles security' is a sentence assessors hear weekly and accept never.

Across revisions

New in Rev. 3 with no direct Rev. 2 counterpart requirement; Rev. 2 reached external services only obliquely, through external-system connection limits and contract flow-down machinery outside the requirement catalog.

Mapped practices

Brilliant at the Basics practices that support this requirement

IT-04 — Flexible technology stackIT

Partial implementation supportModerate confidence

Why: A stack built for swap forces deliberate external-service management: capabilities are chosen against defined criteria, adopted with exit paths, and replaceable when a provider's security posture degrades — which supplies the selection discipline and the leverage that this requirement's provider obligations depend on.

What this does not claim: May partially address the requirement: swap-ability creates the conditions for imposing security requirements on providers, but the imposing itself — contractual obligations, documented oversight, defined user roles per service — is separate work the practice does not perform. A replaceable service with no security terms in its agreement leaves the requirement's core untouched.

Practice-side activities

Evaluate providers against defined security criteria before adoption
Keep exit and migration paths current so provider obligations remain enforceable in practice

Evidence this produces

Adoption decision records showing the security criteria applied
The service register with exit paths and internal owners

Review status: Pending NIST SME review · Reviewed by Brilliant at the Basics editorial — practitioner-authored; NIST SME review pending · updated 2026-08-06

Doing the work

Implementation considerations and evidence

Implementation considerationsIndependent guidance — tailor to your environment

Inventory the external services touching CUI first; the count is nearly always higher than expected once file transfer, e-signature, and support tooling are included.
Put the security requirements in the agreement — flow-down clauses, federal authorization baselines where applicable, breach-notification terms; a provider's marketing page is not a contractual obligation.
Assign each service an internal owner who reviews the provider's attestations and configuration on a cadence — oversight is a named person's job, not a procurement checkbox.

What operating evidence looks likeRecords worth retaining, not a submission checklist

The external-service inventory with CUI relevance, provider obligations, and internal owner per service
Agreements or terms showing security requirements imposed on providers
Dated oversight records: attestation reviews, configuration checks, service reviews

Suggested owners, derived from the mapped practices and artifacts: IT leader · Procurement lead. Ownership is a named person in your organization, not a role on a website.

Artifacts

Templates and worksheets with a mapped relationship

QUESTIONNAIRE · REVIEW ANNUAL RE-ISSUE FOR CRITICAL SUPPLIERS; AT ONBOARDING FOR EVERY NEW SUPPLIERSupplier Security Questionnaire

The other revision

Where this came from in Rev. 2

No direct Rev. 2 counterpart — this requirement is new in Rev. 3. Open the transition crosswalk →

Provenance

Sources and review status

Primary sources	NIST SP 800-171 Rev. 3 — Protecting CUI in Nonfederal Systems · NIST SP 800-171A Rev. 3 — Assessing Security Requirements for CUI
Review status	Pending NIST SME review
Content version	1.0
Updated	2026-08-06