SC-7(26): Classified National Security System Connections

SC-7(26) requires you to block any direct connection between a classified national security system (CNSS) and an external network unless the connection passes through an approved, defined protective mechanism (the control’s organization-defined parameter). In practice, you must enforce boundary architecture, routing rules, and connection approvals that make “direct” paths impossible, and you must keep evidence that the prohibition is continuously effective. ¹

Key takeaways:

• Treat this as an architectural prohibition: no route, circuit, tunnel, or wireless bridge may create a direct CNSS-to-external path. ¹
• Define and approve the required intermediary protection (the control parameter), then force all external connectivity through it. ¹
• Audit readiness hinges on evidence: diagrams, approved connection lists, device configs, rule reviews, and exception handling records. ¹

The sc-7(26): classified national security system connections requirement is short, but it drives real engineering work. The control’s intent is to prevent “accidental internet” scenarios for classified environments by banning direct CNSS connections to external networks unless you route through a specified protective capability that your organization defines and authorizes. ¹

For a CCO or GRC lead, the fastest way to operationalize SC-7(26) is to treat it like a boundary control with three moving parts: (1) scope what counts as the classified system boundary and what counts as “external,” (2) name the only allowed connection pattern (the intermediary protection), and (3) prove through technical controls and recurring checks that no other paths exist. ¹

This page gives requirement-level implementation guidance: who owns what, the steps to implement, the artifacts assessors ask for, and the failure modes that trigger findings. It is written for operators who need to get to a defensible posture quickly and keep it that way through change, procurement, and incident response.

Regulatory text

Requirement (verbatim): “Prohibit the direct connection of a classified national security system to an external network without the use of {{ insert: param, sc-07.26_odp }}.” ¹

What the operator must do:

1. Prohibit direct connections between a CNSS and any external network path. This means you must prevent connectivity patterns where traffic can flow from CNSS components to an external network without passing through a defined protective control point. ¹
2. Define the “use of” mechanism (the organization-defined parameter). Your program must specify what intermediary protection is required (for example: a particular boundary gateway stack, cross-domain solution, proxy/guard, or other authorized mediation) and require it for any permitted connectivity. ¹
3. Enforce it technically and procedurally. Policies alone do not satisfy this. You need network architecture, routing segmentation, device configuration, and change control that make direct paths infeasible. ¹

Practical translation: “No CNSS system gets a raw pipe to anything ‘outside.’ If it must connect, it connects only through the specific approved boundary protection you named, and you can prove that’s true.” ¹

Plain-English interpretation (what counts as “direct” and “external”)

“Direct connection” is any path that bypasses your approved protective mediation. Don’t overthink cabling. Assessors look for actual reachability: routed paths, VPN tunnels, misconfigured firewall rules, dual-homed hosts, unmanaged modems, cellular hotspots, Wi‑Fi bridges, and “temporary” maintenance connections that became permanent.

“External network” is anything outside the CNSS authorization boundary. That includes:

• Enterprise IT networks not part of the CNSS boundary
• Third-party networks (integrators, OEM support, cloud services)
• Partner interconnects
• Any internet-connected segment

Your key operational job is to document these definitions in your environment so engineering and auditors interpret them consistently.

Who it applies to

SC-7(26) applies when you have a classified national security system and any requirement or temptation to connect it to networks outside its boundary. This commonly shows up in:

• Federal information systems with classified workloads
• Contractor-operated environments handling federal data where classified systems exist in scope for the program control set ¹

Operationally, you will touch multiple teams:

• Network engineering (segmentation, firewalling, routing, WAN)
• Security engineering (boundary protections, monitoring)
• ISSO/ISSM or system security leadership (authorization boundary decisions)
• Change management (approvals, emergency changes)
• Third-party risk / supplier management (remote support and interconnects)

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

Use this sequence to get from requirement to enforceable reality.

1) Set the control parameter (define the required protection)

SC-7(26) includes an organization-defined parameter (“{{ insert: param, sc-07.26_odp }}”). Decide what must sit between CNSS and any external network.

Operator outputs:

• A written standard that names the approved mediation pattern(s)
• Technical minimums for that mediation (for example: firewall + proxy + inspection, guard, managed boundary enclave)

Keep the definition specific enough that an engineer can build to it and an assessor can test it.

2) Establish the CNSS boundary and classify connection types

You need a definitive list of:

• Systems and subnets inside the CNSS boundary
• Boundary enforcement points
• All external networks and interconnects

Tactical move that saves time: create a connection inventory with a simple decision: Allowed only through approved mediation vs Prohibited.

3) Architect to remove “direct path” failure modes

Focus on eliminating the common ways direct connections appear:

• No dual-homing: prevent hosts from bridging CNSS and non-CNSS networks.
• No unmanaged wireless: enforce wireless controls so no CNSS endpoint can join external networks outside the defined boundary protection.
• No ad hoc remote access: block inbound management paths that bypass boundary mediation.

4) Implement enforcement controls (make it technically impossible)

At minimum, build these into your operating environment:

Network controls

• Routing and ACL rules that prevent CNSS-to-external transit except through the defined boundary mediation
• Firewall policy with default-deny for external egress paths from CNSS segments
• Explicit allow-lists for required destinations, ports, and protocols that are mediated

System controls

• Host firewall policies preventing secondary network interfaces or unauthorized VPN clients
• Endpoint restrictions on tethering/hotspots where relevant

Process controls

• Connection approval workflow that requires security sign-off and architecture review before any new interconnect is implemented
• Standard build templates for boundary devices so teams don’t “one-off” their way into exceptions

5) Put recurring verification on a calendar (and tie it to change)

Auditors will ask how you ensure the prohibition remains true after changes.

Build recurring checks into:

• Firewall rule reviews focused on CNSS egress and management access paths
• Network scanning/route validation to confirm no unintended paths exist
• Configuration compliance checks for boundary devices and CNSS endpoints

6) Control third-party connectivity explicitly

Most “direct connections” arrive through third parties: integrators, OEM maintenance, and troubleshooting.

Require that third-party access:

• Terminates in a controlled boundary point you approved
• Is time-bounded and logged
• Cannot create split tunneling or lateral paths around mediation

If you use a tool like Daydream for third-party due diligence workflows, connect SC-7(26) to third-party onboarding so network interconnect requests cannot proceed without the required architecture, approvals, and evidence attachments.

Required evidence and artifacts to retain

Keep artifacts that prove (a) your definition, (b) your architecture, and (c) continuous enforcement.

Minimum evidence set (practical):

• Policy/standard defining the required protective mediation for CNSS external connections (maps to the control parameter) ¹
• Network diagrams showing CNSS boundary, external networks, and mediation points
• Connection inventory listing each external connection, its purpose, and the mediation path
• Firewall/ACL configurations or exported rule sets demonstrating default-deny and explicit allowed paths
• Change records for new/modified connections with approvals and implementation details
• Recurring review logs (rule review tickets, scan reports, route validation outputs)
• Exception register (if any), including compensating controls and time limits

Common exam/audit questions and hangups

Expect questions like:

• “Show me every external connection from the CNSS and the boundary point it traverses.”
• “How do you know there is no direct path via a dual-homed system or maintenance link?”
• “Where is the organization-defined parameter documented, and how is it enforced in builds?”
• “What happens when a third party requests remote access for support?”
• “How do emergency changes get reviewed after implementation?”

Hangup pattern: teams can describe the architecture but can’t produce a complete connection inventory plus configs that match the diagram.

Frequent implementation mistakes (and how to avoid them)

Mistake	Why it fails SC-7(26)	How to avoid it
“Policy says no direct connections” but no technical enforcement	Assessors test reachability, not intent 1	Enforce with routing, ACLs, and boundary device configs; keep exports/screenshots.
Undefined control parameter	The requirement explicitly depends on the organization-defined mediation 1	Write the standard, name the approved pattern, and link it to the SSP and architecture.
Forgotten “temporary” links (cellular modem, Wi‑Fi, bench network)	Creates an unmediated external path	Maintain an inventory; require security sign-off for any non-standard connectivity.
Third-party remote support bypasses boundary	Common real-world backdoor	Contractually and technically force access through the approved boundary, with logging and time limits.
Diagrams don’t match configs	Findings come from mismatches	Make diagram updates part of the change ticket definition of done.

Enforcement context and risk implications

No public enforcement cases were provided in the supplied source catalog for SC-7(26). Treat the risk as mission and national security impact: a direct CNSS-to-external connection reduces containment and increases the chance that malware, misconfiguration, or unauthorized access crosses the boundary without passing through approved controls. ¹

From an assessment standpoint, SC-7(26) findings often expand beyond a single control. A “direct connection” can cascade into boundary protection weaknesses, incomplete system boundary definitions, and change control gaps.

Practical 30/60/90-day execution plan

First 30 days (stabilize and define)

• Assign a control owner and engineering owner for SC-7(26).
• Define the organization-required mediation (the control parameter) and publish it as a standard. ¹
• Build an initial CNSS boundary diagram and external network list.
• Create a draft connection inventory; flag unknowns as issues to close.

By 60 days (enforce and inventory)

• Implement routing/ACL/firewall changes that block non-mediated paths.
• Remove or remediate dual-homed hosts and unmanaged wireless bridges.
• Formalize the connection approval workflow with required artifacts (diagram update, security approval, config evidence).
• Integrate third-party access requests into the same workflow (procurement + security + network).

By 90 days (prove and maintain)

• Start recurring verification (rule reviews, route validation, config compliance checks) and store outputs.
• Run a tabletop for “urgent support request from a third party” and validate that the process prevents bypass paths.
• Prepare an assessor-ready evidence packet: standard, diagrams, inventory, configs, tickets, and review logs.
• If you track controls in Daydream, map SC-7(26) to the owner, procedure, and recurring evidence artifacts so audits become a packaging exercise, not a scramble. ¹

Frequently Asked Questions

What should we put in the organization-defined parameter for SC-7(26)?

Define the specific approved boundary mediation that must be used for any CNSS-to-external connectivity, and document it in an enforceable standard. The parameter should be testable: an assessor should be able to confirm traffic traverses that control point. ¹

Does “external network” include our corporate network?

Yes if the corporate network is outside the CNSS authorization boundary. Treat any non-CNSS enterprise segment as external unless you have explicitly included it in the boundary documentation and controls. ¹

Are one-way data transfers still “connections” under SC-7(26)?

If a transfer mechanism creates a path between the CNSS and an external network, assess it as a connection and require the approved mediation. Document the architecture and show how the mediation prevents a direct path. ¹

How do we handle third-party remote support without violating SC-7(26)?

Require third-party access to terminate at the approved boundary mediation, with explicit approvals, logging, and time limits. Block ad hoc VPNs, cellular hotspots, and split-tunnel configurations that create bypass routes.

What evidence is most persuasive in an audit?

A complete connection inventory tied to current network diagrams, plus exported firewall/ACL configurations proving default-deny and explicit mediated allows. Pair that with change tickets and recurring review records that show the prohibition stays effective over time.

We have no external connections today. Do we still need to implement SC-7(26)?

Yes. Document the prohibition, confirm there are no paths (including wireless and maintenance links), and keep evidence that the environment is configured to prevent direct connectivity if someone tries to add it through change. ¹

Footnotes

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