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CA-3(5) Security Assessment

Restrictions on External System Connections

High Risk Moderate Medium Cost

CA-3(5) (Restrictions on External System Connections) enhances base CA-3 within the NIST Assessment, Authorization, and Monitoring family. Base CA-3 sets the foundational expectation; this enhancement adds specificity: This enhancement strengthens CA-3 with requirements for restrictions on external system connections in environments that create, receive, maintain, or transmit ePHI. Covered entities and business associates apply it to security assessments, authorizations, continuous monitoring, and POA&M tracking for systems that handle ePHI.

Control Objective

Implement Restrictions on External System Connections so organization-defined assessment, authorization, and monitoring safeguards operate consistently on systems and networks that handle ePHI, with measurable evidence for HIPAA and NIST assessments.

Implementation Guidance

  1. Map CA-3(5) to systems in scope (EHR, imaging, lab, pharmacy, billing, identity, backups, and BA connections).\n2. Translate “Restrictions on External System Connections” into technical settings, procedures, or architecture patterns owned by named roles.\n3. Prefer enforceable controls (config, automation, mediation) over awareness-only measures where feasible.\n4. Integrate with change, incident, and downtime processes so clinical operations are not surprised.\n5. Log and retain evidence of operation (tickets, configs, test results) aligned to audit needs.\n6. Include vendors/BAs in contracts and connection standards when they touch the control surface.\n7. Test after major EHR, network, or cloud changes — upgrades often reset protections.\n8. Review exceptions at least quarterly; expire “temporary” holes that expose ePHI paths.

Real-World Use Cases

How this control shows up in healthcare and HIPAA-covered environments.

Real-world scenario

Independent EHR assessment (CA-3(5))\nA team independent of the build group assesses access and audit controls before go-live authorization. Evidence labeled for CA-3(5).\n\n### Specialized medical-device review (CA-3(5))\nFocused assessment covers IoMT segmentation and remote vendor paths into clinical networks. Evidence labeled for CA-3(5).\n\n### Leverage HIE SOC2 results (CA-3(5))\nExternal assessment results are reused carefully with gap analysis for local ePHI interfaces. Evidence labeled for CA-3(5).

Best Practices

  • Name an owner for CA-3(5) in the SSP control matrix.\n- Favor system enforcement on ePHI paths over informal email approval.\n- Measure coverage: percent of in-scope clinical systems where the enhancement operates.\n- Review exceptions quarterly with security and clinical informatics.\n- Feed relevant events to SIEM with a named use case.\n- Keep a one-page evidence pack (config + sample log + last test) ready for assessors.

Common Gaps & Violations

  • Policy cites CA-3(5) but production EHR/network paths show no enforcement of restrictions on external system connections.\n- Permanent exceptions with no expiry for vendors or “special” clinics.\n- Control implemented only on corporate IT — clinical devices and interfaces omitted.\n- No logs or test records; reliance on tribal knowledge.\n- Major upgrade silently disabled the enhancement.

Required Documentation

  • Procedure/standard for Restrictions on External System Connections (CA-3(5))\n- Architecture or configuration baselines showing enforcement points\n- Exception register with owners and expiry\n- Sample logs, alerts, or test results\n- Training or runbook references for clinical/IT operators

How to Test & Validate

  1. Attempt a prohibited or out-of-policy action related to restrictions on external system connections; confirm block, alert, or required workflow.\n2. Complete an authorized clinical/IT path; confirm success and logging.\n3. Sample open exceptions for approval and expiry.\n4. Verify at least one EHR-adjacent and one BA/vendor path are in scope.\n5. Confirm evidence retained for the last 90 days (or per policy).

Audit Considerations

Assessors look for operating evidence of Restrictions on External System Connections on systems touching ePHI — configs, logs, restore/DR artifacts, or failed-test results — not only a policy paragraph referencing CA-3(5).

HIPAA Mapping

How this NIST control supports HIPAA Security Rule expectations.

  • 164.308(a)(8) Evaluation — periodic technical and nontechnical evaluation of security measures for ePHI.\n- 164.308(a)(1)(ii)(A) Risk Analysis — assessments inform how ePHI is at risk.\n- 164.308(a)(1)(ii)(B) Risk Management — authorize and monitor controls that reduce ePHI risk.\n- 164.316(b)(1) Documentation — retain assessment and authorization evidence as required.

Compliance Tips

  • List CA-3(5) explicitly in the system security plan with system inventory references.\n- Prioritize emergency department, inpatient EHR, and remote access paths first.\n- Bundle evidence with related HIPAA evaluation, integrity, or workforce-security narratives where they overlap.

References & Resources

  • NIST SP 800-53 Rev. 5 — CA-3(5)\n- Related controls: CA-3, SC-7(5)

Related Guidelines

Related controls that commonly accompany CA-3(5).

CA-3 High

System Interconnections

CA-3 requires authorizing connections from the system to other systems, documenting interface characteristics and security requirements…
SC-7(5) High

Deny by Default — Allow by Exception

SC-7(5) (Deny by Default — Allow by Exception) enhances base SC-7 within the NIST System and Communications Protection family. Base SC-7…
CA-1 High

Security Assessment Policy and Procedures

CA-1 requires policy and procedures for assessment, authorization, and monitoring — purpose, scope, roles, management commitment…

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