NIST SP 800-53 Rev. 5 AC-3(3) — Mandatory Access Control

What this control requires

Organizations must enforce a mandatory access control (MAC) policy, uniformly applied across all subjects and objects. The policy constrains subjects from passing information to unauthorized entities, granting privileges to others, or modifying security attributes. Subjects may be granted specific privileges that bypass these constraints. This control supports the Governance capability within the Access Control family.

In plain English

Organizations must enforce a mandatory access control (MAC) policy, uniformly applied across all subjects and objects. 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-3(3)) 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.
• Mandatory. 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.
• Scope: management, attributes, access control, information, mandatory access control, capability, privileges, organizations.

Evidence to collect

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

Signed policy or standard documents the safeguard. Focus: Mandatory Access Control.

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-3(4) — Discretionary Access Control
• Control AC-4(20) — Approved Solutions
• Control AC-4(24) — Internal Normalized Format
• Control AC-4(26) — Audit Filtering Actions
• Control AC-4(27) — Redundant/Independent Filtering Mechanisms
• Control AC-4(1) — Object Security And Privacy Attributes

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control AC-3(3)

Topics: governance riskpolicy management