CA-9: Internal System Connections

The ca-9: internal system connections requirement means you must formally authorize every internal connection into your system boundary (for example, links to corporate networks, shared services, internal APIs, management planes, and enclaves) and be able to prove that authorization during an assessment. Treat each internal connection like a controlled interface: documented, approved by the right owner, and kept current as architecture changes. ¹

Key takeaways:

• Maintain an inventory of internal connections mapped to your system boundary and data flows.
• Implement a standard authorization workflow (risk review + approval + conditions) before connections go live.
• Retain repeatable evidence: diagrams, approvals, firewall rules, monitoring, and periodic reauthorization records.

CA-9 is easy to misunderstand because “internal” sounds low-risk. In practice, internal connections are where systems quietly inherit risk: a production environment connected to an enterprise identity service, a logging pipeline shared across business units, an internal API gateway, a management subnet, or a “temporary” network link that becomes permanent. CA-9 forces discipline around these pathways by requiring explicit authorization of internal connections to the system. ²

For a Compliance Officer, CCO, or GRC lead, the operational goal is straightforward: you need a defensible list of what’s connected, who approved it, what security conditions apply, and how you keep the list accurate as infrastructure changes. Assessors rarely fail teams for lacking a perfect diagram; they fail teams for having no authoritative inventory, no approvals, or approvals that don’t match reality.

This page gives requirement-level implementation guidance you can hand to control owners (network, cloud platform, security engineering) and then audit with confidence. It focuses on fast operationalization: define what “internal connection” means in your environment, establish an authorization gate, and produce evidence that stands up in a NIST SP 800-53 Rev. 5 assessment.

Regulatory text

Requirement (excerpt): “Authorize internal connections of {{ insert: param, ca-09_odp.01 }} to the system;” ¹

Operator interpretation: You must (1) identify the set of internal systems, services, and network segments that connect to your system, (2) decide which of those connections are allowed, and (3) record an explicit authorization for each allowed connection before or as it operates. The parameter in the excerpt indicates your organization defines the specific “internal connections” in scope (for example, by connection type, system class, or boundary). ¹

Plain-English interpretation of CA-9

CA-9 requires a positive allow-list posture for internal connectivity into your system boundary. If something inside your enterprise can reach your system (network path, API integration, identity federation, shared admin tooling), you need an approval record that says: “this connection is intended, reviewed, and permitted under stated conditions.”

CA-9 is not satisfied by “we’re on the corporate network” or “it’s behind the firewall.” It expects an authorization decision and traceable evidence.

Who it applies to

Entity scope

• Federal information systems implementing NIST SP 800-53 controls. ²
• Contractor systems handling federal data where NIST SP 800-53 is a contractual or program requirement. ²

Operational context (where CA-9 shows up)

• Systems with a defined authorization boundary (ATO-style boundary or equivalent control boundary).
• Environments with shared internal services: IdP, SIEM, EDR, vulnerability scanners, configuration management, backup, DNS, time services, CI/CD, container registries, secrets management, enterprise service buses, internal API gateways.
• Multi-account / multi-subscription cloud estates where “internal” means “within the same org,” not necessarily “within the same VPC/VNet.”

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

Step 1: Define “internal connection” for your system boundary

Write a short scoping statement that your operators can apply consistently. Include at least:

• Connection types: network connectivity (L3/L4), application/API integrations, identity and directory trust, shared management access, shared data pipelines.
• Direction: inbound to the system, outbound from the system, and bidirectional links. (Even if you focus CA-9 on “to the system,” auditors will ask about both once diagrams appear.)
• System boundary: what is “the system” and what is “internal but external to the boundary.”

Deliverable: “CA-9 Internal Connection Scope” section in the SSP or system control narrative. ²

Step 2: Build an internal connection inventory (authoritative list)

Create a register that becomes the single source of truth. Minimum fields that work in practice:

• Connection ID
• Source system/service (owner, environment)
• Destination system component (owner, environment)
• Purpose / business justification
• Data types involved (high level)
• Technical path (network segments, ports/protocols, API endpoints, trust relationships)
• Security controls/conditions (e.g., mTLS, IP allowlist, MFA for admins, PAM, encryption)
• Approval status, approver, approval date
• Review cadence trigger (e.g., “on material change” and “periodic review”)

Practical tip: tie this inventory to change management tickets so it stays alive.

Step 3: Establish an authorization workflow (the “gate”)

CA-9 is an authorization control. Define who can approve what, and what checks must occur before approval. A simple, defensible model:

Approval roles

• System Owner (or delegate): approves business justification and boundary impact.
• Security (ISO/CISO delegate): confirms required safeguards are specified.
• Network/Platform owner: confirms routing/firewall/security group changes align to the request.

Minimum checks before approval

• Connection appears on the inventory/register.
• Diagram/data flow updated or attached.
• Required safeguards selected from a standard list (examples below).
• Monitoring/logging expectations documented for the interface.

Deliverable: “Internal Connection Authorization Procedure” (a 1–2 page SOP) and a ticket template that captures required fields.

Step 4: Implement technical enforcement consistent with the authorization

Authorization without implementation is a common audit failure. For each authorized connection, ensure the technical reality matches the approved conditions:

• Firewall rules / security groups / NACLs match the declared source, destination, and ports.
• API gateway policies match the declared client identity and scopes.
• Identity federation (trusts, SAML/OIDC apps) matches intended relying parties.
• Management plane connectivity (bastions, VPN, PAM workflows) is restricted to approved administrative sources.

Deliverable: configuration evidence (screenshots or exports), and a mapping from each inventory entry to its control points.

Step 5: Monitor and detect unauthorized internal connections

CA-9 expects you to control internal connectivity; in practice, you also need detection so you can prove the control operates:

• Periodic review of firewall/security group changes against the approved register.
• Alerts for new routes/peering, newly opened ports, or new API clients.
• Reconciliation between architecture diagrams, CMDB/cloud inventory, and the CA-9 register.

Deliverable: monitoring rule list or alert evidence tied to internal connection change events.

Step 6: Reauthorize on change (and periodically)

Define triggers that force reauthorization:

• New integration or new calling system
• Changed data types
• Changed trust model (new identity provider, new network path, new peering)
• Material change to encryption/authentication

Deliverable: reapproval records linked to change tickets.

Required evidence and artifacts to retain

Auditors test CA-9 by sampling connections and asking you to show they were authorized and implemented. Keep these artifacts in a well-labeled control evidence folder:

Core artifacts

• CA-9 control narrative (SSP/control description) with scope definition. ²
• Internal Connection Inventory/Register (current version + change history).
• Network/data flow diagrams showing internal interfaces and boundary crossings.
• Authorization records (tickets, sign-offs, email approvals if unavoidable, meeting minutes with decision).
• Configuration evidence:
  • Firewall/security group rules
  • API gateway policies
  • IAM trust relationships for integrations
  • VPN/peering configuration summaries

Operational artifacts

• Change management records that created/modified a connection.
• Periodic reconciliation reports (even a spreadsheet diff is better than nothing).
• Exceptions register for any temporary connections, with end dates and compensating controls you actually implemented.

Common exam/audit questions and hangups

Assessors tend to ask the same things repeatedly:

1. “Show me all internal connections to the system.” They want a list, not a narrative.
2. “Pick three connections. Prove they were authorized.” Expect sampling.
3. “Does your diagram match your firewall rules?” Inconsistency is a red flag.
4. “How do you prevent ‘shadow’ connections?” They are testing whether CA-9 is operational or only documented.
5. “What triggers reauthorization?” They want change-driven governance.

Hangup: teams treat “internal” as out of scope and over-focus on external connections. CA-9 is explicitly about internal connections. ¹

Frequent implementation mistakes and how to avoid them

Mistake	Why it fails	How to avoid it
No authoritative inventory	You cannot prove completeness	Create a register and tie it to change tickets; make it the review artifact
Approvals exist but don’t specify conditions	Authorization becomes meaningless	Require ports/protocols, identity method, and logging requirements in the approval template
Diagrams are stale	Auditors compare diagrams to configs	Put diagram update as a required step in the connection request workflow
“Temporary” connections never expire	Expands attack paths over time	Track exceptions with owners and explicit removal triggers in change management
Only network teams are involved	APIs/identity/shared services create internal connections too	Expand scope definition to include application and identity trust connections

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so you should treat CA-9 primarily as an assessment readiness and risk-reduction control, not an enforcement-driven control in this write-up.

Risk implications are still concrete: unauthorized internal connections widen lateral movement paths, create undocumented data flows, and break boundary assumptions used in your ATO/security plan. CA-9 reduces that risk by requiring explicit decisions and traceability for internal pathways. ²

A practical 30/60/90-day execution plan

First 30 days (Immediate: establish control footing)

• Name a CA-9 control owner and backups (usually GRC with network/platform execution owners).
• Draft the scope definition for “internal connection” for your system boundary and publish it in the SSP/control narrative. ²
• Stand up a connection register (spreadsheet is acceptable to start) and populate it with known connections from architecture diagrams, cloud inventories, and firewall/security group exports.
• Create a standard authorization ticket template with required fields and approvers.

Days 31–60 (Near-term: make it operational)

• Run a reconciliation workshop with network, platform, and application owners: identify unknown connections and either authorize them or plan removal.
• Implement the authorization gate in your change workflow so new/changed connections cannot go live without the CA-9 fields completed.
• Attach at least one artifact to each register entry: diagram snippet, config export, or approval ticket.

Days 61–90 (Ongoing: prove repeatability)

• Establish a recurring reconciliation routine tied to existing operational rhythms (change advisory board, monthly architecture review, or cloud security review).
• Create a sampling-ready evidence pack: pick several high-risk connections and preassemble “authorization + config + monitoring” bundles.
• If you use Daydream, map CA-9 to an assigned owner, documented procedure, and recurring evidence artifacts so collection is repeatable and assessor-ready. ¹

Frequently Asked Questions

What counts as an “internal connection” for CA-9 in cloud environments?

Treat any connectivity or trust that crosses your system boundary as an internal connection, even if it stays within your company’s cloud org. Common examples include VPC/VNet peering, shared identity providers, shared logging pipelines, and internal API clients.

Do we need written approvals for every internal firewall rule?

You need authorization for each internal connection to the system. In practice, group related firewall rules under a single connection record when they represent one logical interface, and ensure the approval captures the full intended scope (sources, destinations, ports, and conditions). ¹

Can we satisfy CA-9 with a network diagram and a policy statement?

Not reliably. Auditors typically expect evidence of an authorization decision (who approved, when, and under what conditions) plus proof the implemented configuration matches that decision.

How does CA-9 relate to third-party access?

CA-9 is about internal connections, but third-party pathways often traverse internal systems (for example, a third party connects to an internal jump host that connects to your system). Document and authorize the internal segments under CA-9, and manage the third-party portion under your third-party risk and access controls.

What’s the fastest way to find unknown internal connections?

Start with exports from firewalls/security groups and cloud network topology, then reconcile against known application integrations and identity trusts. Unknown paths should be either authorized with conditions or removed through change management.

What evidence is most persuasive in an assessment?

A register entry that ties together (1) an approval ticket, (2) a diagram or data flow, and (3) a config artifact (firewall/security group/API policy) is usually enough to demonstrate the control is both designed and operating.

Footnotes

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

2. NIST SP 800-53 Rev. 5