AC-21 AC · Access Control

Information Sharing

LOW ✓ MODERATE ✓ HIGH
2 Enhancements 1 Overlay 7 Related Controls
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Requirements NIST SOURCE

Discussion (NIST Supplemental Guidance)

Information sharing applies to information that may be restricted in some manner based on some formal or administrative determination. Examples of such information include, contract-sensitive information, classified information related to special access programs or compartments, privileged information, proprietary information, and personally identifiable information. Security and privacy risk assessments as well as applicable laws, regulations, and policies can provide useful inputs to these determinations. Depending on the circumstances, sharing partners may be defined at the individual, group, or organizational level. Information may be defined by content, type, security category, or special access program or compartment. Access restrictions may include non-disclosure agreements (NDA). Information flow techniques and security attributes may be used to provide automated assistance to users making sharing and collaboration decisions.

Enhancements NIST SOURCE

AC-21(1) Automated Decision Support LOW MODERATE HIGH

Employ [automated mechanisms] to enforce information-sharing decisions by authorized users based on access authorizations of sharing partners and access restrictions on information to be shared.

Discussion

Automated mechanisms are used to enforce information sharing decisions.

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AC-21(2) Information Search and Retrieval LOW MODERATE HIGH

Implement information search and retrieval services that enforce [information-sharing restrictions].

Discussion

Information search and retrieval services identify information system resources relevant to an information need.

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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-21 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. information-sharing circumstances where user discretion is required to determine whether access authorizations assigned to a sharing partner match the information�s access and use restrictions are defined;
  2. automated mechanisms or manual processes that assist users in making information-sharing and collaboration decisions are defined;
  3. authorized users are enabled to determine whether access authorizations assigned to a sharing partner match the information�s access and use restrictions for <AC-21_ODP[01] information-sharing circumstances>;
  4. <AC-21_ODP[02] automated mechanisms> are employed to assist users in making information-sharing and collaboration decisions.

Examine

[SELECT FROM: Access control policy; procedures addressing user-based collaboration and information sharing (including restrictions); system design documentation; system configuration settings and associated documentation; list of users authorized to make information-sharing/collaboration decisions; list of information-sharing circumstances requiring user discretion; non-disclosure agreements; acquisitions/contractual agreements; system security plan; privacy plan; privacy impact assessment; security and privacy risk assessments; other relevant documents or records].

Interview

[SELECT FROM: Organizational personnel responsible for information-sharing/collaboration decisions; organizational personnel with responsibility for acquisitions/contractual agreements; system/network administrators; organizational personnel with information security and privacy responsibilities].

Test

[SELECT FROM: Automated mechanisms or manual process implementing access authorizations supporting information-sharing/user collaboration decisions].

Overlays

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)

STIGs & CCIs

No STIG checks or CCI mappings are currently loaded for AC-21. 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.

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Evidence

Potential Evidence — Derived

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

Policy

  • Access control policy
  • system security plan
  • privacy plan

Configuration

  • system design documentation
  • system configuration settings and associated documentation

Testing

  • Automated mechanisms or manual process implementing access authorizations supporting information-sharing/user collaboration decisions

Other Records

  • procedures addressing user-based collaboration and information sharing (including restrictions)
  • list of users authorized to make information-sharing/collaboration decisions
  • list of information-sharing circumstances requiring user discretion
  • non-disclosure agreements
  • acquisitions/contractual agreements
  • privacy impact assessment
  • security and privacy risk assessments
  • other relevant documents or records