NIST SP 800-53 Rev. 5 AC-3(15) — Discretionary And Mandatory Access Control

What this control requires

Organizations must enforce both a mandatory access control (MAC) policy and a discretionary access control (DAC) policy over the defined subjects and objects in the system. Implementing both policies provides additional protection against unauthorized code execution by users or processes, preventing a single compromised user or process from affecting the entire system. This control supports the Governance capability within the Access Control family.

In plain English

Organizations must enforce both a mandatory access control (MAC) policy and a discretionary access control (DAC) policy over the defined subjects and objects in the system. 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(15)) 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.
• Discretionary. Document the trigger, the owner and the cadence.
• Process. Document the trigger, the owner and the cadence.
• Scope: management, access control, mandatory access control, system, protection, 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: Discretionary And 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) 164.310(a)(2)(iii) — Facility Access Controls - Access Control and Validation Procedures
• BSI C5:2020 AM-02 — Acceptable Use and Safe Handling of Assets Policy

Related controls in NIST SP 800-53 Rev. 5

• Control AC-3(3) — Mandatory Access Control
• Control AC-4(5) — Embedded Data Types
• Control AC-4(4) — Flow Control Of Encrypted Information
• Control AC-3(4) — Discretionary Access Control
• Control AC-4(20) — Approved Solutions
• Control AC-6 — Least Privilege

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control AC-3(15)

Topics: governance riskpolicy management