NIST SP 800-53 Rev. 5 AC-4(20) — Approved Solutions

What this control requires

Organizations must employ defined solutions in approved configurations to control the flow of specified information across security domains. These solutions and configurations are outlined in cross-domain policies and guidance, tailored to the types of information flows across classification boundaries. This control supports the Governance capability within the Access Control family.

In plain English

Organizations must employ defined solutions in approved configurations to control the flow of specified information across security 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.

This control is rated critical in the source catalogue. Treat gaps here as production incidents in the risk register, not housekeeping.

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-4(20)) and look for objective evidence on the latest two assessment cycles.

How to implement

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.
• Information. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Domain. Document the trigger, the owner and the cadence.
• Scope: management, access control, information, domains, solutions, capability, organizations, policy.

Evidence to collect

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

Signed policy or standard documents the safeguard. Focus: Approved Solutions.

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) 164.308(a)(4)(ii)(A) — Information Access Management - Isolating Healthcare Clearinghouse Functions
• ISO/IEC 27001:2022 A.5.1 — Policies for information security
• BSI C5:2020 SP-01 — Documentation, communication and provision of policies and instructions
• ISO/IEC 27701:2025 A.3.3 — Information security policies

Related controls in NIST SP 800-53 Rev. 5

• Control AC-4(27) — Redundant/Independent Filtering Mechanisms
• Control AC-4(24) — Internal Normalized Format
• Control AC-4(26) — Audit Filtering Actions
• Control AC-4(30) — Filter Mechanisms Using Multiple Processes
• Control AC-3(3) — Mandatory Access Control
• Control AC-4(2) — Processing Domains

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control AC-4(20)

Topics: governance riskpolicy management