NIST SP 800-53 Rev. 5 CA-9 — Internal System Connections

What this control requires

Authorizes, documents, and reviews internal system connections, specifying interface characteristics, security requirements, and conditions for termination. This control supports the Internal Connection Manager capability within the Assessment, Authorization, and Monitoring family.

In plain English

Authorizes, documents, and reviews internal system connections, specifying interface characteristics, security requirements, and conditions for termination. In practice, this means you can prove you policy management-level controls on a defined cadence.

Why it matters

SP 800-53 is the catalogue every U.S. federal authorisation (FedRAMP, FISMA, CMMC) and most regulated industries point at. A missing control surfaces as a Plan of Action & Milestones (POA&M) item that an Authorizing Official must approve before the Authority To Operate is granted or renewed.

This control is rated high. Auditors expect a named owner, a remediation SLA, and a tooling artefact that evidences continuous operation.

What an auditor looks for

A 3PAO (FedRAMP) or Independent Assessor (NIST RMF) tests against NIST SP 800-53A assessment procedures. For each control they expect a documented implementation that addresses every assessment objective (Examine, Interview, Test) and an implementation summary in the System Security Plan.

Within Assessment, Authorization, and Monitoring, the assessor will trace your implementation back to the catalogue reference (Control CA-9) and look for objective evidence on the latest two assessment cycles.

How to implement

Policy Management

Docs. Keep each policy in version-controlled Markdown alongside the code that implements it; ship a signed PDF snapshot at each annual review and link the SHA into the SoA.

Operational checklist

• Policy. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Internal. Document the trigger, the owner and the cadence.
• Termination. Document the trigger, the owner and the cadence.
• System. Document the trigger, the owner and the cadence.
• Scope: management, conditions, authorization, reviews, system, termination, assessment, system connections.

Evidence to collect

• Policy Document. A signed and version-controlled policy / standard / procedure document.

Signed policy or standard documents the safeguard. Focus: Internal System Connections.

Common pitfalls

• Policies that no engineer has read; the version in Confluence drifts from the version that's actually being enforced.

How it maps to other frameworks

Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.

• HIPAA (45 CFR Part 164) 164.308(a)(3)(ii)(C) — Workforce security - Establish Termination Procedures
• ISO/IEC 27001:2022 A.8.26 — Application security requirements
• NIST SP 800-171 Rev. 3 3.12.1 — Security Assessment
• BSI C5:2020 SP-01 — Documentation, communication and provision of policies and instructions

Related controls in NIST SP 800-53 Rev. 5

• Control CA-3 — Information Exchange
• Control CA-1 — Policy And Procedures
• Control CA-6(1) — Joint Authorization -- Intra-Organization
• Control CA-6(2) — Joint Authorization -- Inter-Organization
• Control CA-7(4) — Risk Monitoring
• Control CA-2(1) — Independent Assessors

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control CA-9

Topics: governance riskpolicy management