AC-4(21)_physical-or-logical-separation-of-information-flows

DevOps & Security

Separate information flows logically or physically using [organization-defined] to accomplish [organization-defined].

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/NIST/SP800-53_rev5/AC_access-control/AC-4(21)_physical-or-logical-separation-of-information-flows/SKILL.md

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AC-4(21) Physical or Logical Separation of Information Flows

Enhancement of: AC-4

High-Level Description

Family: Access Control (AC) Framework: NIST SP 800-53 Rev 5

Enforcing the separation of information flows associated with defined types of data can enhance protection by ensuring that information is not commingled while in transit and by enabling flow control by transmission paths that are not otherwise achievable. Types of separable information include inbound and outbound communications traffic, service requests and responses, and information of differing security impact or classification levels.

What to Check

Verify AC-4(21) Physical or Logical Separation of Information Flows is documented in SSP
Confirm control is operating effectively
Review evidence of continuous monitoring for AC-4(21)
Verify enhancement builds upon base control AC-4

How to Test

Step 1: Review Documentation

Examine the System Security Plan (SSP) and related artifacts for AC-4(21) implementation details. Verify the organization has documented how this control is satisfied.

Step 2: Validate Implementation

# For cloud environments, use cloud-audit-mcp tools
# For on-premises, review system configurations directly

# Example: Check if account management policies exist
grep -r "account.management\|access.control" /etc/security/ 2>/dev/null

Step 3: Test Operating Effectiveness

Verify the control is actively functioning, not just documented. Check logs, configurations, and operational evidence.

Tools

Tool	Purpose	Usage
cloud-audit-mcp	Check IAM policies and access controls	`cloud_audit_iam_policies`
hackbrowser-mcp	Test web application access controls	`browser_auth_test`

Remediation Guide

Control Statement

Separate information flows logically or physically using [organization-defined] to accomplish [organization-defined].

Implementation Guidance

Risk Assessment

Finding	Severity	Impact
AC-4(21) Physical or Logical Separation of Information Flows not implemented	High	Access Control
AC-4(21) partially implemented	Medium	Incomplete Access Control

CWE Categories

CWE ID	Title
CWE-284	Improper Access Control

References

Checklist

Control documented in SSP
Implementation evidence collected
Operating effectiveness validated
Continuous monitoring in place
Related controls (SC-32) reviewed