SC-7(27): Unclassified Non-national Security System Connections

The sc-7(27): unclassified non-national security system connections requirement is a network boundary rule that auditors expect you to prove with architecture and configuration evidence, not policy language. The control’s intent is straightforward: unclassified systems (that are not national security systems) cannot connect “directly” to the internet or other external networks if the connection bypasses your approved boundary protections. If a system can reach an external network without passing through a controlled security choke point, you have a gap.

For a CCO or GRC lead, the work is less about selecting new tools and more about eliminating unknown network paths, standardizing how external connectivity is provided, and documenting enforcement. In practice, this commonly shows up in three places: (1) legacy sites with unmanaged circuits, (2) cloud workloads with permissive egress routes, and (3) third-party interconnects (partners, service providers, MSPs) that were provisioned as “temporary” but became permanent.

This page translates SC-7(27) into a fast operational plan: scope, technical actions, required artifacts, and the exam questions you will get.

Regulatory text

Control requirement (excerpt): “Prohibit the direct connection of {{ insert: param, sc-07.27_odp.01 }} to an external network without the use of {{ insert: param, sc-07.27_odp.02 }}.” ¹

What the operator must do: interpret the placeholders as (a) the defined set of unclassified non-national security system components or networks in your environment, and (b) the boundary protection mechanism(s) you designate as mandatory. You then enforce this as a technical prohibition: no routes, circuits, VPNs, peering, or wireless paths may provide external connectivity that bypasses your boundary protections. Document the decision: what is “in scope,” what counts as an “external network,” and what boundary protections are approved. ²

Plain-English interpretation

• “Unclassified Non-national Security System”: systems that process unclassified information and are not designated national security systems. Treat them as “federal/business systems” that still require strong boundary controls.
• “Direct connection … to an external network”: any network path where traffic can flow from the system (or its subnet) to the internet, a partner network, a carrier-managed network, or another external environment without being forced through your managed security boundary.
• “Without the use of [boundary protection]”: the connection is only allowed if it is mediated by the specific boundary protections you approve (examples in practice: controlled gateways, firewalls, secure web gateways, proxy layers, dedicated boundary enclaves, inspected VPN termination, or cloud egress controls), and those protections are configured and monitored as part of your control environment.

Who it applies to

Entities

• Federal information systems implementing NIST SP 800-53 controls. ²
• Contractor systems handling federal data where NIST SP 800-53 is flowed down contractually or used to satisfy a federal program requirement. ²

Operational contexts where SC-7(27) commonly triggers findings

• Multi-site networks where smaller offices have local internet breakout.
• Cloud VPC/VNet architectures with “default route to internet gateway” and no enforced egress inspection.
• Partner connectivity (B2B VPN, MPLS, private cross-connect) that lands inside internal networks instead of terminating in a boundary segment.
• Developer and admin “temporary” tunnels, split-tunnel VPN, or unmanaged remote access paths.

What you actually need to do (step-by-step)

1) Define the three scoping statements (write them down)

Create a short scoping memo that your technical team can execute:

1. In-scope systems/components: which UNNS systems, subnets, and endpoints are covered by SC-7(27).
2. External networks: what you classify as external (internet, third-party networks, partner environments, non-org cloud tenants, carrier networks not under your control).
3. Approved boundary protections: the required technical controls that must mediate any external connectivity.

This document becomes your audit “north star” and prevents arguments about what “direct” means mid-assessment.

2) Build a connectivity inventory you can prove

You need a list of every external connection path for in-scope systems:

• Internet egress points (on-prem and cloud)
• Inbound exposures (public IPs, load balancers, exposed services)
• Third-party links (VPNs, private circuits, peering)
• Remote access solutions and their split/full-tunnel behavior

Practical tip: require network engineering to attest that the list is complete, then validate with routing tables, firewall rulebases, and cloud route tables.

3) Identify “direct” paths (the gap list)

Flag any of the following as presumptive noncompliance until proven otherwise:

• A subnet with a route to an internet gateway/NAT that is not forced through your security stack
• A partner VPN that terminates on an internal router rather than a boundary firewall/VPN concentrator in a controlled zone
• A site with local breakout that bypasses corporate egress inspection
• Cloud security group rules and NACLs that permit broad inbound access without boundary mediation

Deliverable: a gap register entry per path with owner and remediation action.

4) Enforce boundary mediation (technical remediation patterns)

Choose the pattern that fits your architecture, then standardize it:

On-prem patterns

• Force all external traffic through a central egress protected by firewalls and proxy/security gateways.
• Terminate third-party VPNs in a DMZ/boundary segment, not in internal networks.
• Use routing and ACLs to prevent alternate paths (deny-by-default for outbound at local sites unless through the boundary).

Cloud patterns

• Centralize egress via inspected NAT / firewall appliances or cloud-native egress controls.
• Remove direct internet gateways from workloads that should not have them; route through a shared services security VPC/VNet.
• Require private connectivity to third parties to terminate in a controlled boundary subnet with enforced inspection and logging.

Your goal: a diagram and configuration set that makes “bypass the boundary” architecturally hard, and operationally detectable.

5) Add exception handling that is technical, time-bound, and reviewable

If any direct connection must temporarily exist (e.g., migration constraints), treat it as an exception:

• documented business justification
• compensating controls (extra monitoring, restricted ports, isolation)
• defined expiration and a removal plan
• approval by the system owner and security authority

Auditors will accept exceptions more readily when they are narrow, time-bound, and tracked like risk.

6) Prove continuous enforcement

SC-7(27) is easy to pass once and fail later due to drift. Add recurring checks:

• configuration compliance checks on firewalls/route tables
• periodic discovery of new public IPs, new VPNs, and new egress points
• change management gates that prevent new external connections without security architecture review

Daydream fit (where it earns its place): use Daydream to map SC-7(27) to a single control owner, a written implementation procedure, and a recurring evidence checklist so audits don’t depend on tribal knowledge during staff turnover.

Required evidence and artifacts to retain

Keep artifacts that prove (a) you know the paths, (b) you enforced mediation, and (c) you detect drift:

1. Network architecture diagrams showing boundary zones and all external connections for in-scope systems.
2. Data flow diagrams for key systems that show where external networks are involved.
3. Firewall/VPN gateway configurations (exports or read-only screenshots) showing termination points and rules that prevent bypass.
4. Routing evidence: route tables (on-prem core and cloud route tables) showing forced path through boundary protections.
5. Egress control evidence: proxy/SWG configuration, egress firewall policies, and logging destinations.
6. Asset and connection inventory: list of third-party interconnects, public IPs, and exposed services tied to approvals.
7. Exception register with approvals, compensating controls, and expiration dates.
8. Change management tickets for any new/modified external connections, with security review notes.

Common exam/audit questions and hangups

Expect assessors to ask:

• “Show me all external connections for this system and where they terminate.”
• “How do you prevent a team from adding a direct internet gateway or site breakout?”
• “Which devices are your approved boundary protections, and how do you know traffic always traverses them?”
• “Do third-party VPNs land in a DMZ/boundary segment or inside internal networks?”
• “How do you detect new external exposure introduced by cloud changes?”

Hangups that cause delays:

• diagrams that don’t match configs
• unclear definition of “external network”
• exceptions with no expiry, or “temporary” connections older than anyone can explain

Frequent implementation mistakes and how to avoid them

1. Mistake: Treating this as a policy-only control.
   Fix: lead with enforced routing and termination architecture, then align policy.

2. Mistake: Missing partner/third-party interconnects in scope.
   Fix: reconcile carrier invoices, VPN concentrator configs, and cloud attachments against your inventory.

3. Mistake: Allowing cloud workload teams to self-provision direct egress.
   Fix: enforce guardrails (approved network modules, restricted IAM, and routing standards) plus periodic discovery.

4. Mistake: “DMZ” in name only.
   Fix: validate segmentation with ACLs, firewall policies, and routing rules that prevent lateral movement.

5. Mistake: Exceptions that never close.
   Fix: require an expiry and a concrete decommission task in the same ticket.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this specific control enhancement, so don’t frame this as a fine-avoidance exercise. Treat it as an assessment and breach-risk control: direct external connections expand attack surface, complicate monitoring, and increase the odds that security teams miss or cannot contain intrusion paths. Align SC-7(27) with SC-7 boundary protection governance and your broader network security standard. ²

Practical execution plan (30/60/90-day)

First 30 days (stabilize and scope)

• Assign a control owner (network/security architecture) and a GRC owner for evidence.
• Publish the scoping memo: in-scope UNNS systems, what counts as external, approved boundary protections.
• Build the initial external connection inventory and gap list.
• Freeze new external connections pending review, or add an expedited security review gate.

Days 31–60 (remediate highest-risk paths)

• Eliminate or reroute the clearest “direct” paths (local breakouts, unmanaged VPN terminations, permissive cloud routes).
• Standardize a reference architecture for third-party connections (boundary termination + segmentation + logging).
• Stand up exception handling with approvals, compensating controls, and expiry tracking.

Days 61–90 (make it durable and auditable)

• Implement recurring drift detection (config checks, route table reviews, discovery of new public exposure).
• Tie external connectivity changes to change management with mandatory security sign-off.
• Package your evidence set (diagrams, configs, inventories, exceptions) and run a mock interview with the system/network owners.
• In Daydream, map SC-7(27) to the owner, the procedure, and the recurring evidence artifacts so future audits are repeatable.

Frequently Asked Questions

What counts as an “external network” for SC-7(27)?

Treat any network not under your organization’s direct administrative control as external, including the public internet and third-party networks. Write your definition down and apply it consistently across on-prem, cloud, and partner connectivity.

Does SC-7(27) ban all internet connectivity for unclassified systems?

No. It bans direct connectivity that bypasses your approved boundary protections. Internet access can exist if it is mediated through your defined gateways and monitored.

Are private circuits (MPLS, cross-connects) considered “direct connections”?

They can be. If the circuit lands inside internal networks without terminating in a controlled boundary segment, you have the same bypass problem as a direct internet link.

How do we handle cloud workloads that need outbound access to SaaS APIs?

Route egress through your approved cloud egress controls (central firewall, inspected NAT, or proxy pattern) and block alternate default routes. Keep route table and policy evidence to prove enforcement.

What evidence is most persuasive to an auditor?

Config and routing evidence that demonstrates forced traversal through boundary protections, backed by current diagrams. Pair that with an inventory of external connections and an exception log.

We have a “temporary” VPN for a third party. Is an exception enough?

An exception can work if it is time-bound, approved, and paired with compensating controls and a removal plan. If it has no expiry or monitoring, expect it to be treated as a control failure.

Footnotes

1. NIST SP 800-53 Rev. 5 OSCAL JSON

2. NIST SP 800-53 Rev. 5