NIST SP 800-171 Rev. 3·Requirement 3.1.3·high·Component: Access Control

What this control requires

This control ensures that approved authorizations are enforced to regulate the flow of Controlled Unclassified Information (CUI) within systems and across interconnected systems. It covers preventing CUI from being transmitted in the clear, blocking unauthorized external communications, and restricting inter-organizational transfers based on specific data structures and content. Enforcement mechanisms include the use of encryption, filtering devices, and trust-based security measures. This control supports the Flow Control Enforcement Mechanism capability within the Access Control (3.1) family.
— NIST SP 800-171 Rev. 3, Requirement 3.1.3

In plain English

This control ensures that approved authorizations are enforced to regulate the flow of Controlled Unclassified Information (CUI) within systems and across interconnected systems. In practice, this means you can prove you access enforcement-level controls on a defined cadence.

Why it matters

DoD contractors and their subcontractors must implement all 100 SP 800-171 requirements to keep CUI handling contracts. Gaps are scored against the SPRS scoring methodology; below a 110-point starting score, each unmet requirement deducts points and a below-threshold score can disqualify a bid.

This control is rated high. Auditors expect a named owner, a remediation SLA, and a tooling artefact that evidences continuous operation.

What an auditor looks for

A C3PAO conducting a CMMC Level 2 assessment uses NIST SP 800-171A objectives. They expect a System Security Plan (SSP), Plan of Action & Milestones (POA&M) for any gaps, and objective evidence (configurations, ticket records, training records) for every requirement.

Within Access Control, the assessor will trace your implementation back to the catalogue reference (Requirement 3.1.3) and look for objective evidence on the latest two assessment cycles.

How to implement

Endpoint Protection

MDM. Make MDM enrollment a hard gate for device access (Intune compliance + Conditional Access, or Jamf + Okta device trust). Unmanaged devices simply don't get a session token.

EDR. Deploy CrowdStrike / SentinelOne / Defender for Endpoint to every server and laptop; alert on any host that stops sending telemetry for >24h.

Operational checklist

  • Access. Document the trigger, the owner and the cadence.
  • Information. Document the trigger, the owner and the cadence.
  • Access Control. Document the trigger, the owner and the cadence.
  • Protection. Document the trigger, the owner and the cadence.
  • Security. Document the trigger, the owner and the cadence.
  • Scope: enforcement, flow enforcement, cui, content, security, clear, encryption, access control.

Evidence to collect

  • User Device Scan. MDM compliance state per user device (Intune / Jamf / Workspace ONE).

Endpoint compliance telemetry (Intune, Jamf) proves managed coverage. Focus: Information Flow Enforcement.

Common pitfalls

  • Pilot MDM rollouts that quietly exclude executives or engineers; carving out the highest-risk users is the most common audit failure.

How it maps to other frameworks

Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.

Related controls in NIST SP 800-171 Rev. 3

References

Topics: endpoint securitydata protectionendpoint protectionencryption at rest