# NIST SP 800-171 Rev. 3 3.16.3 — External System Services - Source: https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-16-3-external-system-services - Section: [Compliance](https://support.icompaas.com/compliance) › [NIST SP 800-171 Rev. 3 Requirements](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3) › System and Services Acquisition — §3.16 - Last updated: 2026-06-05 - Publisher: iCompaas, Inc. (https://www.icompaas.com) **NIST SP 800-171 Rev. 3**·Requirement `3.16.3`·high·Component: **Planning** ## What this control requires > This control requires that external service providers, who process, store, or transmit Controlled Unclassified Information (CUI), comply with defined security requirements. It also involves defining and documenting user roles and responsibilities, including shared responsibilities with external service providers, and implementing processes to monitor ongoing security compliance. This control supports the External Service Compliance capability within the Planning (3.16) family. > > — NIST SP 800-171 Rev. 3, Requirement 3.16.3 ### In plain English This control requires that external service providers, who process, store, or transmit Controlled Unclassified Information (CUI), comply with defined security requirements. In practice, this means you can prove you information management-level controls on a defined cadence. ## Why it matters DoD contractors and their subcontractors must implement all 100 SP 800-171 requirements to keep CUI handling contracts. Gaps are scored against the SPRS scoring methodology; below a 110-point starting score, each unmet requirement deducts points and a below-threshold score can disqualify a bid. 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 C3PAO conducting a CMMC Level 2 assessment uses NIST SP 800-171A objectives. They expect a System Security Plan (SSP), Plan of Action & Milestones (POA&M) for any gaps, and objective evidence (configurations, ticket records, training records) for every requirement. Within **Planning**, the assessor will trace your implementation back to the catalogue reference (Requirement 3.16.3) and look for objective evidence on the latest two assessment cycles. ## How to implement #### Logging Monitoring **AWS.** Org-trail CloudTrail to a central log archive account, GuardDuty in every region, and Security Hub for cross-source correlation. **Azure.** Pipe every diagnostic setting into a central Log Analytics workspace; onboard Microsoft Sentinel for SIEM/SOAR. **GCP.** Aggregate audit logs in a dedicated logging project with sink to BigQuery; enable Security Command Center Premium and route findings to Chronicle SIEM. #### 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 - **Information.** Document the trigger, the owner and the cadence. - **System.** Document the trigger, the owner and the cadence. - **Monitor.** Document the trigger, the owner and the cadence. - **Risk.** Document the trigger, the owner and the cadence. - **Security.** Document the trigger, the owner and the cadence. - **Scope:** management, store, cui, security, service providers, system services. ## Evidence to collect - **Vendor Risk Management.** `vendor_risk_management` evidence - **Policy Document.** A signed and version-controlled policy / standard / procedure document. Third-party risk management evidence (assessments, contracts, due diligence) shows supplier oversight. Signed policy or standard documents the safeguard. Focus: External System Services. ## Common pitfalls - Per-account logging that nobody stitches together at the org level — incidents that cross accounts go undetected for days. - 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. - [**ISO/IEC 27001:2022 A.5.19** — Information security in supplier relationships](https://support.icompaas.com/compliance/iso-27001-2022/a-5-19-information-security-in-supplier-relationships) - [**NIST SP 800-53 Rev. 5 SA-9** — External System Services](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sa-9-external-system-services) - [**CIS Controls v8 15.6** — Monitor Service Providers](https://support.icompaas.com/compliance/cis-controls-v8/15-6-monitor-service-providers) - [**BSI C5:2020 PS-01** — Physical Security and Environmental Control Requirements](https://support.icompaas.com/compliance/bsi-c5-2020/ps-01-physical-security-and-environmental-control-requirements) ## Related controls in NIST SP 800-171 Rev. 3 - [**Requirement 3.11.1** — Risk Assessment](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-11-1-risk-assessment) - [**Requirement 3.16.2** — Unsupported System Components](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-16-2-unsupported-system-components) - [**Requirement 3.4.11** — Information Location](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-4-11-information-location) - [**Requirement 3.17.2** — Acquisition Strategies, Tools, and Methods](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-17-2-acquisition-strategies-tools-and-methods) - [**Requirement 3.1.9** — System Use Notification](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-1-9-system-use-notification) - [**Requirement 3.15.1** — Policy and Procedures](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-15-1-policy-and-procedures) ## References - [NIST Computer Security Resource Center — NIST SP 800-171 Rev. 3](https://csrc.nist.gov/pubs/sp/800/171/r3/final) - Catalogue identifier: `Requirement 3.16.3` Topics: governance riskvendor riskvendor managementsupply chain securitylogging monitoringpolicy management ## Related compliance guidance - [NIST SP 800-171 and CMMC: a practical guide to protecting CUI in the cloud](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3): Start with the full NIST SP 800-171 implementation guide — scope, roadmap, evidence and how the assessment runs. - [NIST SP 800-53 Rev. 5: a practical implementation guide for cloud teams](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5): The catalogue 800-171 is tailored from, and the basis of the FedRAMP Moderate baseline your cloud providers must meet for CUI. - [ISO/IEC 27001:2022 compliance: a practical implementation guide](https://support.icompaas.com/compliance/iso-27001-2022): If commercial customers ask for a certificate as well, most 800-171 controls can be evidenced once and mapped to Annex A.