NIST SP 800-53 Rev. 5 AC-4(28) — Linear Filter Pipelines

What this control requires

When transferring information between different security domains, organizations must implement a linear content filter pipeline, enforced with both discretionary and mandatory access controls. This control supports the Governance capability within the Access Control family.

In plain English

When transferring information between different security domains, organizations must implement a linear content filter pipeline, enforced with both discretionary and mandatory access controls. In practice, this means you can prove you access 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(28)) and look for objective evidence on the latest two assessment cycles.

How to implement

1. Write a short policy stating intent, scope and named owner.
2. Encode it as a platform guardrail — SCP, Azure Policy initiative, Organisation Policy, or repository policy.
3. Wire a monitoring signal that catches drift (CSPM rule, SIEM rule, scheduled query, Workspace alert) and ticket it.
4. Review on a documented cadence and capture the review in the risk register or compliance tracker.

Operational checklist

• 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.
• Information. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Scope: management, access control, information, domains, filter pipelines, controls, identity, review.

Evidence to collect

• Identity Scan. IAM / IdP exports — Entra ID, Okta, IAM Identity Center, Workspace directory — showing accounts, roles, MFA state and last sign-in.

Identity analytics (Okta, SailPoint, Access Analyzer) demonstrates least-privilege. Focus: Linear Filter Pipelines.

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 3.1.11 — Session Termination
• CIS Controls v8 6.7 — Centralize Access Control
• ISO/IEC 27001:2022 A.5.2 — Information security roles and responsibilities
• SOC 2 (2017 TSC) CC6.1 — Logical Access Controls
• BSI C5:2020 PS-04 — Physical site access control

Related controls in NIST SP 800-53 Rev. 5

• Control AC-4(22) — Access Only
• Control AC-3(8) — Revocation Of Access Authorizations
• Control AC-6(2) — Non-Privileged Access For Nonsecurity Functions
• Control AC-14 — Permitted Actions Without Identification Or Authentication
• Control AC-3(2) — Dual Authorization
• Control AC-4(32) — Process Requirements For Information Transfer

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control AC-4(28)

Topics: identity accessidentity managementaccess reviewprivileged accessdevsecops