CMMC Navigatorby Foxx Cyber Bedrock CMMC

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3.4.6Turn off what you do not need

Systems run the minimum set of functions the job requires.

The requirement, verbatim

NIST SP 800-171 Rev. 2 · 3.4.6

Employ the principle of least functionality by configuring organizational systems to provide only essential capabilities.

Requirement 3.4.6, practice name in the CMMC assessment guide: Least Functionality.

NIST's discussion

Systems can provide a wide variety of functions and services. Some of the functions and services routinely provided by default, may not be necessary to support essential organizational missions, functions, or operations. It is sometimes convenient to provide multiple services from single system components. However, doing so increases risk over limiting the services provided by any one component. Where feasible, organizations limit component functionality to a single function per component.

Organizations review functions and services provided by systems or components of systems, to determine which functions and services are candidates for elimination. Organizations disable unused or unnecessary physical and logical ports and protocols to prevent unauthorized connection of devices, transfer of information, and tunneling. Organizations can utilize network scanning tools, intrusion detection and prevention systems, and end-point protections such as firewalls and host-based intrusion detection systems to identify and prevent the use of prohibited functions, ports, protocols, and services.

NIST SP 800-171 Rev. 2, discussion under 3.4.6. Whitespace normalised; wording unchanged.

Assessment objectives

An assessor decides each of these separately. The requirement is met only when every objective is.

  1. [a] essential system capabilities are defined based on the principle of least functionality
  2. [b] the system is configured to provide only the defined essential capabilities

NIST SP 800-171A, determination statements for 3.4.6.

For assessors: examine, interview, test

NIST SP 800-171A names what an assessor may examine, whom they may interview, and what they may test for this requirement. Assessors select from these lists; they are not a checklist of everything you must produce.

Examine
  • Configuration management policy
  • configuration management plan
  • procedures addressing least functionality in the system
  • system security plan
  • system design documentation
  • system configuration settings and associated documentation
  • security configuration checklists
  • other relevant documents or records
Interview
  • Personnel with security configuration management responsibilities
  • personnel with information security responsibilities
  • system or network administrators
Test
  • Organizational processes prohibiting or restricting functions, ports, protocols, or services
  • mechanisms implementing restrictions or prohibition of functions, ports, protocols, or services

NIST SP 800-171A, potential assessment methods and objects for 3.4.6.

Evidence

No evidence examples are published for this requirement yet. The objectives above are what an assessor checks; evidence is whatever shows each one is true in your environment, dated and kept with your system security plan.

Scoring weight

Worth 5 points. Not meeting this requirement subtracts 5 from your 110-point SPRS score. These are the requirements with the largest effect on your posture.

DoD NIST SP 800-171 Assessment Methodology v1.2.1 weighting, as carried in the Bedrock scoring table. The score starts at 110 and subtracts the weight of every requirement not met.

In Rev. 3

Rev. 2 is what your contract requires today. A standing DoD class deviation keeps Rev. 2 in force; NIST has published Rev. 3, but it is not adopted for contracts. In Rev. 3 this requirement is reworded: 03.04.06 Least Functionality. It gains organization-defined parameters.

See the Rev. 2 and Rev. 3 wording word by word, or start with the status page.

Where this page's facts come from
Requirement text
bedrock-cmmc-api@89b8e8e:migrations/004_reference_requirements.sql#Requirement.basicRequirement@rev2
Discussion
bedrock-cmmc-api@89b8e8e:migrations/004_reference_requirements.sql#Requirement.discussion@rev2
Practice name
bedrock-cmmc-api@89b8e8e:migrations/004_reference_requirements.sql#Requirement.title@rev2 (CMMC Assessment Guide practice name)
Objectives
bedrock-cmmc-api@89b8e8e:migrations/005_reference_objectives.sql#AssessmentObjective.description@rev2
Examine, interview, test
bedrock-cmmc-api@89b8e8e:migrations/005_reference_objectives.sql#AssessmentObjective.description@rev2 ({examineGuidance, interviewGuidance, testGuidance})
Level
bedrock-cmmc-api@89b8e8e:migrations/021_fix_level1_requirements.sql#Requirement.cmmcLevel@rev2
Weight
bedrock-cmmc-api@89b8e8e:internal/cmmc/requirement_values.go#requirementValues (DoD AM v1.2.1 / eMASS L2 template v3.8)
Rev. 3 mapping
bedrock-cmmc-api@89b8e8e:docs/reference/nist-800-171-rev3/normalized/r2_r3_transition_map.json#r2_to_r3
Plain-language title and summary
editorial/CMMC Navigator.dc.html#RAW (Foxx Cyber editorial)