NIST SP 800-53 Rev. 5 AC-6(4) — Separate Processing Domains

What this control requires

Implement separate processing domains using virtualization, physical separation, or hardware/software mechanisms to enable finer-grained allocation of user privileges, restricting access across domains. This control supports the Virtualization System capability within the Access Control family.

In plain English

Implement separate processing domains using virtualization, physical separation, or hardware/software mechanisms to enable finer-grained allocation of user privileges, restricting access across domains. In practice, this means you can prove you policy management-level controls on a defined cadence.

Why it matters

SP 800-53 is the catalogue every U.S. federal authorisation (FedRAMP, FISMA, CMMC) and most regulated industries point at. A missing control surfaces as a Plan of Action & Milestones (POA&M) item that an Authorizing Official must approve before the Authority To Operate is granted or renewed.

What an auditor looks for

A 3PAO (FedRAMP) or Independent Assessor (NIST RMF) tests against NIST SP 800-53A assessment procedures. For each control they expect a documented implementation that addresses every assessment objective (Examine, Interview, Test) and an implementation summary in the System Security Plan.

Within Access Control, the assessor will trace your implementation back to the catalogue reference (Control AC-6(4)) and look for objective evidence on the latest two assessment cycles.

How to implement

Physical Security

Inheritance. For cloud-only operations, inherit physical controls from the provider's SOC 2 / ISO 27001 report and document the inheritance in the SoA.

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

• Policy. Document the trigger, the owner and the cadence.
• Access. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Enable. Document the trigger, the owner and the cadence.
• Physical. Document the trigger, the owner and the cadence.
• Scope: management, access control, domains, system, user privileges, virtualization, hardware, software.

Evidence to collect

• Policy Document. A signed and version-controlled policy / standard / procedure document.

Signed policy or standard documents the safeguard. Focus: Separate Processing Domains.

Common pitfalls

• 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.

• NIST SP 800-171 Rev. 3 3.1.5 — Least Privilege
• HIPAA (45 CFR Part 164) 164.310(a)(2)(iii) — Facility Access Controls - Access Control and Validation Procedures
• ISO/IEC 27001:2022 A.7.14 — Secure disposal or re-use of equipment

Related controls in NIST SP 800-53 Rev. 5

• Control AC-4(21) — Physical Or Logical Separation Of Information Flows
• Control AC-4(27) — Redundant/Independent Filtering Mechanisms
• Control AC-4(30) — Filter Mechanisms Using Multiple Processes
• Control AC-16(9) — Attribute Reassignment - Regrading Mechanisms
• Control SC-49 — Hardware-Enforced Separation And Policy Enforcement
• Control AC-4(20) — Approved Solutions

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control AC-6(4)

Topics: governance riskphysical securitypolicy management