NIST SP 800-53 Rev. 5 SC-7(28) — Connections To Public Networks

What this control requires

Prohibit the direct connection of organization-defined systems to a public network, including the Internet and organizational extranets with public access. This helps to mitigate the risk of unauthorized access and ensures the security of sensitive systems. This control supports the Boundary Protection Device capability within the System and Communications Protection family.

In plain English

Prohibit the direct connection of organization-defined systems to a public network, including the Internet and organizational extranets with public access. In practice, this means you can prove you access 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 critical in the source catalogue. Treat gaps here as production incidents in the risk register, not housekeeping.

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(28)) and look for objective evidence on the latest two assessment cycles.

How to implement

Network Security

AWS. VPC Flow Logs to S3, default-deny security groups, AWS Network Firewall for north-south, and Transit Gateway for hub-and-spoke segmentation.

Azure. NSGs with deny-by-default, Azure Firewall Premium with TLS inspection, Private Endpoints for PaaS, and Microsoft Defender for Cloud's secure score for drift.

GCP. VPC Service Controls perimeters around sensitive APIs, Cloud NGFW Enterprise for L7 inspection, Private Service Connect for managed services.

Operational checklist

• Access. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Network. Document the trigger, the owner and the cadence.
• Review. Document the trigger, the owner and the cadence.
• Prohibit. Document the trigger, the owner and the cadence.
• Scope: management, organization, system, protection, identity, review, capability, networks.

Evidence to collect

• Identity Scan. IAM / IdP exports — Entra ID, Okta, IAM Identity Center, Workspace directory — showing accounts, roles, MFA state and last sign-in.

Identity analytics (Okta, SailPoint, Access Analyzer) demonstrates least-privilege. Focus: Connections To Public Networks.

Common pitfalls

• Default-allow egress rules; East-West traffic with no segmentation; jump hosts on the public internet with password auth.

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 3.15.2 — System Security Plan
• CIS Controls v8 9.2 — Use DNS Filtering Services
• ISO/IEC 27001:2022 A.5.2 — Information security roles and responsibilities
• SOC 2 (2017 TSC) CC6.6 — Boundary Protection
• ISO/IEC 27701:2025 A.3.8 — Identity management

Related controls in NIST SP 800-53 Rev. 5

• Control SC-8(5) — Protected Distribution System
• Control AC-11 — Device Lock
• Control PS-4 — Personnel Termination
• Control SC-42(1) — Reporting To Authorized Individuals Or Roles
• Control PE-7 — Visitor Control
• Control SC-7(3) — Access Points

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control SC-7(28)

Topics: identity accessidentity managementaccess reviewprivileged accessnetwork security