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AC-4(28) AC · Access Control

Linear Filter Pipelines

LOW MODERATE HIGH
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Requirements NIST SOURCE

When transferring information between different security domains, implement a linear content filter pipeline that is enforced with discretionary and mandatory access controls.

Discussion (NIST Supplemental Guidance)

Content filtering is the process of inspecting information as it traverses a cross-domain solution and determines if the information meets a predefined policy. The use of linear content filter pipelines ensures that filter processes are non-bypassable and always invoked. In general, the use of parallel filtering architectures for content filtering of a single data type introduces bypass and non-invocation issues.

Implementation Guidance

Engineering Interpretation

Original engineering commentary written for this explorer — not NIST source text and not authoritative guidance.

No engineering interpretation has been authored for AC-4(28) yet. This section is architected to receive it — see the Requirements and Assessment sections above for the authoritative NIST source content in the meantime.

Assessment

NIST SP 800-53A REV 5.2.0

Assessment Objectives

  1. when transferring information between security domains, a linear content filter pipeline is implemented that is enforced with discretionary and mandatory access controls.

Examine

[SELECT FROM: Information flow enforcement policy; procedures addressing information flow enforcement; system design documentation; system configuration settings and associated documentation; system audit records; system security plan; other relevant documents or records].

Interview

[SELECT FROM: Organizational personnel with information flow enforcement responsibilities; system/network administrators; organizational personnel with information security responsibilities].

Test

[SELECT FROM: Mechanisms implementing information flow enforcement functions; mechanisms implementing linear content filters].

Overlays

Showing the OT/ICS overlay for the parent control AC-4 — see the AC-4(28) entries within each baseline below.

OT/ICS Overlay SP 800-82r3

NIST SP 800-82r3 Appendix F, Table 22. Blank baseline means the control/control enhancement is not selected in that initial OT baseline.

LOW

Not applicable at this tier.

MODERATE

  • Base control: Included (matches standard baseline)

HIGH

  • Base control: Included (matches standard baseline)
  • Included: (4)

STIGs & CCIs

No STIG checks or CCI mappings are currently loaded for AC-4(28). This section is architected to display, per product: STIG ID, Finding ID, Severity, Title, Description, Check, Fix, CCI, and NIST control mapping — but nothing is populated here until a real DISA STIG/CCI dataset is ingested.

Learn more about STIG/CCI integration →

Evidence

Potential Evidence — Derived

Categorized from the SP 800-53A "Examine"/"Test" artifact list above by keyword — not an authoritative NIST evidence list.

Policy

  • Information flow enforcement policy
  • system security plan

Configuration

  • system design documentation
  • system configuration settings and associated documentation

Testing

  • Mechanisms implementing information flow enforcement functions
  • mechanisms implementing linear content filters

Other Records

  • procedures addressing information flow enforcement
  • system audit records
  • other relevant documents or records