SA-17(5)_conceptually-simple-design

SA-17(5) Conceptually Simple Design

Enhancement of: SA-17

High-Level Description

Family: System and Services Acquisition (SA) Framework: NIST SP 800-53 Rev 5

The principle of reduced complexity states that the system design is as simple and small as possible (see SA-8(7) ). A small and simple design is easier to understand and analyze and is also less prone to error (see AC-25, SA-8(13) ). The principle of reduced complexity applies to any aspect of a system, but it has particular importance for security due to the various analyses performed to obtain evidence about the emergent security property of the system. For such analyses to be successful, a small and simple design is essential. Application of the principle of reduced complexity contributes to the ability of system developers to understand the correctness and completeness of system security functions and facilitates the identification of potential vulnerabilities. The corollary of reduced complexity states that the simplicity of the system is directly related to the number of vulnerabilities it will contain. That is, simpler systems contain fewer vulnerabilities. An important benefit of reduced complexity is that it is easier to understand whether the security policy has been captured in the system design and that fewer vulnerabilities are likely to be introduced during engineering development. An additional benefit is that any such conclusion about correctness, completeness, and existence of vulnerabilities can be reached with a higher degree of assurance in contrast to conclusions reached in situations where the system design is inherently more complex.

What to Check

• Verify SA-17(5) Conceptually Simple Design is documented in SSP
• Validate all 2 control requirements are implemented
• Confirm control is operating effectively
• Review evidence of continuous monitoring for SA-17(5)
• Verify enhancement builds upon base control SA-17

How to Test

Step 1: Review Documentation

Examine the System Security Plan (SSP) and related artifacts for SA-17(5) 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

Remediation Guide

Control Statement

Require the developer of the system, system component, or system service to: Design and structure the security-relevant hardware, software, and firmware to use a complete, conceptually simple protection mechanism with precisely defined semantics; and Internally structure the security-relevant hardware, software, and firmware with specific regard for this mechanism.

Implementation Guidance

The principle of reduced complexity states that the system design is as simple and small as possible (see SA-8(7) ). A small and simple design is easier to understand and analyze and is also less prone to error (see AC-25, SA-8(13) ). The principle of reduced complexity applies to any aspect of a system, but it has particular importance for security due to the various analyses performed to obtain evidence about the emergent security property of the system. For such analyses to be successful, a small and simple design is essential. Application of the principle of reduced complexity contributes to the ability of system developers to understand the correctness and completeness of system security functions and facilitates the identification of potential vulnerabilities. The corollary of reduced complexity states that the simplicity of the system is directly related to the number of vulnerabilities it will contain. That is, simpler systems contain fewer vulnerabilities. An important benefit of reduced complexity is that it is easier to understand whether the security policy has been captured in the system design and that fewer vulnerabilities are likely to be introduced during engineering development. An additional benefit is that any such conclusion about correctness, completeness, and existence of vulnerabilities can be reached with a higher degree of assurance in contrast to conclusions reached in situations where the system design is inherently more complex.

Risk Assessment

CWE Categories

References

• NIST SP 800-53 Rev 5 - SA-17(5)
• NIST SP 800-53A Rev 5 (Assessment Procedures)
• NIST SP 800-53 Rev 5 Full Catalog

Checklist

• Control documented in SSP
• Implementation evidence collected
• Operating effectiveness validated
• Continuous monitoring in place
• Related controls (AC-25, SA-8, SC-3) reviewed