03.01.03: Information Flow Enforcement

If you handle CUI in a nonfederal environment, information flow enforcement is one of the fastest ways an assessor will separate “we have security tools” from “we control where CUI can go.” 03.01.03 is about preventing CUI from moving to unauthorized destinations, crossing trust boundaries without controls, or being exposed through misrouted integrations, flat networks, over-permissioned identities, or unmanaged third-party connections. ¹

For a CCO or GRC lead, the trap is treating this as a pure network control. In practice, “flow” includes: user-to-system access paths, system-to-system integrations, outbound internet traffic, email and collaboration sharing, administrative pathways, remote access, and data exchanges with third parties (MSPs, SaaS, labs, contract manufacturers, and subcontractors). Your job is to turn that sprawl into: (1) explicit policy rules, (2) enforcement points, and (3) evidence.

This page gives requirement-level guidance you can execute quickly: scoping questions, step-by-step implementation, what artifacts auditors ask for, common failure modes, and a practical 30/60/90 plan tied to SSP/POA&M discipline. ¹

Requirement: 03.01.03 information flow enforcement requirement (what it means)

Plain-English interpretation: You must control how information (especially CUI) is allowed to move across users, devices, networks, applications, and interconnected systems. Define what flows are permitted, implement technical controls that enforce those rules, and document and monitor exceptions so CUI does not “wander” into unauthorized environments. ¹

Think of this as “data path governance.” If a path exists, you either:

• explicitly approve it and enforce it, or
• block it (or remove it), or
• document it as an exception with compensating controls and a POA&M item.

Who it applies to

Applies to nonfederal systems handling CUI, including defense and federal contractors and any organization that processes, stores, or transmits CUI in scope for NIST SP 800-171 Rev. 3 assessments. ¹

Operational contexts where this comes up immediately

• Segmentation between corporate IT and CUI environments
• Remote access (VPN/ZTNA), admin access, and privileged pathways
• SaaS sharing controls (external sharing, guest users, link sharing)
• System integrations (APIs, ETL jobs, SIEM collectors, ticketing, DevOps)
• Third-party access (MSP tooling, subcontractor connectivity, file exchanges)

Regulatory text

Excerpt (as provided): “NIST SP 800-171 Rev. 3 requirement 03.01.03 (Information Flow Enforcement).” ¹

Operator interpretation: NIST expects you to (1) define information flow rules for CUI, (2) implement technical mechanisms that enforce the rules at key control points, and (3) maintain documentation and operating evidence that shows the rules are consistently applied and reviewed. ¹

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

Step 1: Define “flow rules” in a way engineering can implement

Create a CUI Information Flow Policy/Standard with rule statements that are testable. Avoid vague language like “CUI must be protected in transit.” Use statements like:

• “CUI may only be transmitted between the CUI enclave and approved third-party endpoints through managed file transfer with encryption and authenticated users.”
• “Direct outbound internet access from CUI workloads is blocked except for approved update repositories.”
• “External sharing from the CUI collaboration tenant is disabled by default; exceptions require documented approval.”

Deliverable: a short ruleset that maps flows by category:

• User → CUI systems
• CUI system → CUI system (east-west)
• CUI systems → corporate systems
• CUI systems → internet
• CUI systems → third parties

Step 2: Build a flow map and trust boundary diagram you can defend

Create a CUI Data Flow Diagram (DFD) and network/application boundary diagram that identifies:

• where CUI enters your environment
• where it is stored/processed
• all egress paths (email gateways, SFTP, API endpoints, SaaS connectors)
• identity boundaries (IdP tenants, MFA scope, admin consoles)
• third-party access paths (jump hosts, managed tooling, support access)

Practical tip: most teams miss “shadow flows” like browser-based uploads, personal email forwarding, unmanaged USB use, and unsanctioned SaaS sync clients. If you cannot block them everywhere quickly, document them as risks and convert them into explicit backlog items.

Step 3: Select enforcement points (layered controls)

Implement enforcement where it’s hard to bypass:

Network layer

• Segmentation for CUI networks and workloads (VLANs/security groups)
• Egress filtering (deny-by-default outbound where feasible)
• Controlled ingress (only required ports/protocols from known sources)

Identity/access layer

• Conditional access rules for CUI apps and admin portals
• Role-based access that prevents “open access” routes to CUI stores
• Strong controls around service accounts and integration credentials

Application/data layer

• DLP rules for email/collaboration and endpoint upload controls where supported
• SaaS sharing restrictions, tenant-to-tenant controls, and guest access governance
• Approved managed file transfer patterns for external exchanges

Endpoint layer

• Device compliance requirements for access to CUI resources
• Controls limiting unapproved sync clients or removable media pathways (as applicable to your environment)

Deliverable: an “Enforcement Points Register” that lists each rule and the technical control that enforces it.

Step 4: Establish an exception process that doesn’t become a loophole

You need a clean mechanism to approve necessary flows without opening the floodgates.

Minimum exception fields:

• business justification and data classification (CUI type/context)
• source, destination, protocol, authentication method
• expiration date or review trigger
• compensating controls (monitoring, additional authentication, restrictions)
• approval by system owner and security/compliance owner

Tie exceptions to POA&M if they represent a gap you intend to remediate. ¹

Step 5: Instrument logging and routine reviews

Information flow enforcement fails quietly if you don’t watch it.

Operationalize with:

• firewall/security group change logging
• IdP/conditional access policy change logging
• SaaS audit logs for sharing and external access
• alerts for new outbound paths, DNS anomalies, or new integrations (based on your architecture)

Run a recurring review cadence (engineering + security + GRC):

• review rule changes and exceptions
• validate that enforcement is still in place after system changes
• sample test that blocked flows are actually blocked

Step 6: Map to SSP and track gaps in POA&M

For assessment readiness, document:

• SSP control statement for 03.01.03 describing your rules, enforcement points, and monitoring ¹
• responsible owners for each enforcement domain (network, IAM, SaaS, endpoint)
• POA&M items for gaps, with risk rating, target dates, and closure criteria ¹

Daydream (as a workflow, not a tool claim) fits naturally here: treat 03.01.03 as a requirements-to-evidence pipeline, where each flow rule has an owner, a technical enforcement control, and a recurring evidence task that feeds your SSP and POA&M closure checks.

Required evidence and artifacts to retain (assessment-ready)

Keep artifacts that prove both design and operation:

Governance artifacts

• CUI Information Flow Policy/Standard
• CUI boundary, trust boundary, and data flow diagrams
• Enforcement Points Register (rule → control mapping)
• Exception request/approval records and periodic exception reviews

Technical artifacts (screenshots/exports/configs)

• Firewall rules, security group policies, and route controls (exports or screenshots)
• Conditional access/IAM policies for CUI apps and admin portals
• SaaS sharing configuration exports (external sharing settings, guest controls)
• Approved integration inventory with authentication methods and allowed endpoints

Operating evidence

• Change records for rule modifications (tickets/CRs with approvals)
• Logs demonstrating enforcement (blocked connections, denied policy events, DLP hits where applicable)
• Review minutes or sign-offs showing periodic validation
• POA&M entries for gaps plus closure validation evidence ¹

Common exam/audit questions and hangups

Expect questions like:

• “Show me where CUI can flow out of the enclave. What are the allowed egress paths?”
• “How do you prevent users from sharing CUI externally from collaboration tools?”
• “What stops a new integration from sending CUI to an unapproved third party?”
• “How do you detect and approve exceptions? Who signs off?”
• “Demonstrate a test where an unauthorized flow is blocked.”

Hangups that trigger deeper testing:

• Flat networks with broad connectivity and no documented egress rules
• “We rely on training” without technical enforcement
• Diagrams that don’t match reality (assessors will ask engineers, not just GRC)

Frequent implementation mistakes (and how to avoid them)

1. Only documenting a policy. Fix: map each rule to an enforcement point and keep proof of configuration and logs.
2. Treating SaaS as out-of-scope plumbing. Fix: explicitly govern sharing, guest access, and connectors in the flow map.
3. No exception expiry. Fix: require expiration or periodic re-approval and tie long-lived exceptions to POA&M.
4. Forgetting system-to-system flows. Fix: inventory integrations, service accounts, and API endpoints as first-class flows.
5. No ownership model. Fix: name accountable owners per enforcement domain and reflect this in SSP narratives. ¹

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so this page does not cite specific actions.

Risk-wise, weak information flow enforcement commonly leads to:

• CUI sprawl into unmanaged endpoints or tenants
• unauthorized third-party access pathways
• accidental external sharing and misrouted transfers
• inability to prove boundary controls during assessment

For most teams, the business impact shows up as assessment findings, contract friction, delayed awards, or mandated remediation plans, rather than a single “security tool” gap.

Practical 30/60/90-day execution plan

First 30 days (stabilize scope and rules)

• Confirm the CUI boundary and in-scope systems, including SaaS and third-party connections.
• Draft the CUI Information Flow Policy/Standard with a deny-by-default posture for unknown flows.
• Produce an initial data flow diagram and list of known ingress/egress paths.
• Stand up an exceptions workflow with required fields and named approvers.
• Update SSP language for 03.01.03 to reflect current state and planned changes. ¹

Days 31–60 (implement enforcement where bypass risk is highest)

• Implement or tighten network segmentation and egress controls for CUI environments.
• Lock down identity pathways: conditional access, admin restrictions, service account governance.
• Configure SaaS sharing and external access controls aligned to your flow rules.
• Start collecting recurring evidence: policy exports, logs, change tickets, exception approvals.
• Create POA&M entries for gaps you cannot close quickly, with closure criteria. ¹

Days 61–90 (prove operation and make it repeatable)

• Run tabletop tests and technical validation: attempt prohibited flows and document results.
• Perform the first formal exception review and decommission unnecessary pathways.
• Add monitoring/alerting for new egress routes, new integrations, and high-risk sharing events.
• Package evidence for assessors: “rule → enforcement → logs → review” bundles.
• Establish a durable cadence for reviews and SSP/POA&M updates so the control stays true after changes. ¹

Frequently Asked Questions

What counts as an “information flow” for 03.01.03?

Treat any path that can move CUI as a flow: user access, system integrations, outbound internet traffic, email/collaboration sharing, and third-party connections. Your documentation should name sources, destinations, and enforcement points. ¹

Do I need network segmentation to meet the 03.01.03: information flow enforcement requirement?

Segmentation is a common enforcement method, but the requirement is outcome-based: you must control allowed/blocked flows. If you rely on identity and application controls instead, be ready to show how bypass is prevented and how you monitor. ¹

How do I handle required external transfers of CUI to a third party?

Define an approved transfer pattern (managed file transfer, controlled SaaS channel, authenticated access), then block informal paths like ad hoc sharing links. Keep approvals, third-party access scopes, and logs for each transfer mechanism. ¹

What evidence do assessors usually want first?

Start with your data flow diagram, enforcement rule mapping, and configuration exports for your primary enforcement points (firewall/SG, IAM conditional access, SaaS sharing). Then provide logs or tests that show prohibited flows are denied. ¹

We can’t block all flows immediately. Can we document and accept the risk?

Documenting alone rarely satisfies assessors. If you have a temporary gap, place it in a POA&M with compensating controls, target remediation, and closure validation criteria. ¹

How should a GRC team operationalize this without becoming a bottleneck?

Make engineering own enforcement controls, and have GRC own the rulebook, exception governance, and evidence cadence. A workflow system like Daydream helps by assigning each rule to an owner and collecting recurring evidence tied to SSP/POA&M updates.

Footnotes

1. NIST SP 800-171 Rev. 3