NIST SP 800-171 Rev. 3·Requirement 3.1.2·high·Component: Access Control

What this control requires

This control ensures that approved authorizations are enforced for logical access to Controlled Unclassified Information (CUI) and system resources, as per access control policies. It applies to both user and system process access, including remote and external network access, and can extend to applications and services to enhance the protection of CUI. This control supports the Access Enforcement Mechanism capability within the Access Control (3.1) family.
— NIST SP 800-171 Rev. 3, Requirement 3.1.2

In plain English

This control ensures that approved authorizations are enforced for logical access to Controlled Unclassified Information (CUI) and system resources, as per access control policies. In practice, this means you can prove you access management-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 3.1.2) and look for objective evidence on the latest two assessment cycles.

How to implement

Network Security

AWS. VPC Flow Logs to S3, default-deny security groups, AWS Network Firewall for north-south, and Transit Gateway for hub-and-spoke segmentation.

Azure. NSGs with deny-by-default, Azure Firewall Premium with TLS inspection, Private Endpoints for PaaS, and Microsoft Defender for Cloud's secure score for drift.

GCP. VPC Service Controls perimeters around sensitive APIs, Cloud NGFW Enterprise for L7 inspection, Private Service Connect for managed services.

Policy Management

Docs. Keep each policy in version-controlled Markdown alongside the code that implements it; ship a signed PDF snapshot at each annual review and link the SHA into the SoA.

Operational checklist

  • Access. Document the trigger, the owner and the cadence.
  • Information. Document the trigger, the owner and the cadence.
  • Remote. 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.
  • Scope: management, enforcement, remote, external network access, cui, applications, security, access control.

Evidence to collect

  • Policy Document. A signed and version-controlled policy / standard / procedure document.
  • Infra Scan. Continuous infrastructure-posture telemetry — AWS Config, Azure Policy compliance, GCP Organisation Policy, Wiz / Prisma findings.

Signed policy or standard documents the safeguard. Focus: Access Enforcement.

Common pitfalls

  • Default-allow egress rules; East-West traffic with no segmentation; jump hosts on the public internet with password auth.
  • Policies that no engineer has read; the version in Confluence drifts from the version that's actually being enforced.

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: governance riskidentity accessnetwork securitypolicy management