NIST SP 800-53 Rev. 5 SC-7(19) — Block Communication From Non-Organizationally Configured Hosts

What this control requires

Block inbound and outbound communication traffic between organization-defined communication clients that are independently configured by end users and external service providers. This includes instant messaging clients and video conferencing software, while excluding clients configured by the organization for authorized functions. This control supports the Network Traffic Filtering System capability within the System and Communications Protection family.

In plain English

Block inbound and outbound communication traffic between organization-defined communication clients that are independently configured by end users and external service providers. In practice, this means you can prove you security 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 System and Communications Protection, the assessor will trace your implementation back to the catalogue reference (Control SC-7(19)) and look for objective evidence on the latest two assessment cycles.

How to implement

1. Write a short policy stating intent, scope and named owner.
2. Encode it as a platform guardrail — SCP, Azure Policy initiative, Organisation Policy, or repository policy.
3. Wire a monitoring signal that catches drift (CSPM rule, SIEM rule, scheduled query, Workspace alert) and ticket it.
4. Review on a documented cadence and capture the review in the risk register or compliance tracker.

Operational checklist

• Security. Document the trigger, the owner and the cadence.
• Network. Document the trigger, the owner and the cadence.
• Protection. Document the trigger, the owner and the cadence.
• Non-Organizationally. Document the trigger, the owner and the cadence.
• Chain. Document the trigger, the owner and the cadence.
• Scope: management, organization, system, service, functions, protection, software, external service providers.

Evidence to collect

• Vendor Risk Management. vendor_risk_management evidence

Third-party risk management evidence (assessments, contracts, due diligence) shows supplier oversight. Focus: Block Communication From Non-Organizationally Configured Hosts.

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.

• NIST SP 800-171 Rev. 3 3.16.3 — External System Services
• ISO/IEC 27001:2022 A.5.20 — Addressing information security within supplier agreements
• SOC 2 (2017 TSC) P6.1 — Third-Party Disclosure with Data Subject Consent

Related controls in NIST SP 800-53 Rev. 5

• Control SA-9(2) — Identification Of Functions, Ports, Protocols, And Services
• Control CP-2(7) — Coordinate With External Service Providers
• Control SA-5(2) — Security-Relevant External System Interfaces
• Control SC-30(2) — Randomness
• Control SA-9(4) — Consistent Interests Of Consumers And Providers
• Control SC-12(6) — Physical Control Of Keys

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control SC-7(19)

Topics: vendor riskvendor managementsupply chain securitythird party monitoring