Understanding the CUI Data Flow Diagram: A Practical Guide

cui-data-flow-diagram

Controlled Unclassified Information (CUI) is a critical element in the compliance landscape for organizations handling sensitive, unclassified data. A CUI data flow diagram visualizes how CUI enters, moves through, and exits your information systems. In this post, we will explore why a CUI data flow diagram matters, outline steps to create one, and share best practices for ensuring your organization remains compliant with NIST SP 800-171 and CMMC requirements.

What Is a CUI Data Flow Diagram?

A data flow diagram is a graphical representation showing how data moves through an information system: from entry points (external entities) to storage, processing, and exit points. When we refer to a CUI data flow diagram, we specifically map the lifecycle of Controlled Unclassified Information—such as proprietary business data, technical specifications, or other regulated but unclassified information—across people, processes, and technologies.

By documenting the lifecycle of CUI, the diagram highlights areas where additional controls or safeguards (for example, encryption or access restrictions) are required. For defense contractors and companies subject to DFARS clauses, this visibility is critical for demonstrating compliance.

Why You Need a CUI Data Flow Diagram

CMMC/NIST SP 800-171 Alignment

NIST SP 800-171 mandates that organizations protect the confidentiality of CUI. A DFD makes it easier to identify where CUI is stored, transmitted, or processed, and which controls (such as encryption or multi-factor authentication) must be applied at each point.

Risk Identification

By visualizing how CUI moves, you can pinpoint potential vulnerabilities—unsecured transfer paths, shared storage locations, or unmonitored endpoints—before they become a security incident.

Audit and Assessment Support

Auditors and assessors often request detailed documentation of how controlled information is handled. A well-crafted CUI data flow diagram answers many of their questions up front, reducing back-and-forth and accelerating your compliance assessment.

Stakeholder Communication

Data flow diagrams provide a common language for technical staff, compliance officers, and executive leadership. They show, at a glance, how CUI touches various systems without requiring everyone to understand every network topology detail.

Key Components of a CUI Data Flow Diagram

  • External Entities: Sources or destinations outside your network (for example, customers submitting technical specs or third-party service providers).
  • Processes: Any activity where CUI is handled—user authentication, data transformation scripts, application servers, or file transfer services.
  • Data Stores: Repositories where CUI is kept, such as network file shares, databases, backup media, or cloud storage buckets.
  • Data Flows: Labeled arrows indicating the direction and nature of CUI movement (for example, “Upload CUI PDF,” “Retrieve CUI from Database,” or “Encrypted Transmission to Cloud”).

Creating a CUI Data Flow Diagram

Identify All CUI Types


Catalog every kind of CUI your organization handles: drawings, contracts, project plans, technical manuals, and so on. Note where each resides (for example, SharePoint, network drives, or local workstations).

List External Entities
Note all entities that send or receive CUI from your environment. This may include:

  • Defense prime contractors
  • Clients submitting regulated data
  • Government portals or services (for example, eMASS)
  • Third-party software vendors with CUI access

Map Internal Processes
For each CUI type, identify processes or applications that generate, transform, or consume that data. Examples include:

  • User Authentication Process: Employees logging into CUI-enabled systems.
  • Document Management System: Where CUI documents are versioned and tracked.
  • Automated Backups: Scheduled jobs that copy CUI to offline tape or encrypted cloud buckets.

Define Data Stores
Document where each CUI dataset is stored. Common examples include:

  • Encrypted file servers (for example, \FileShare\CUI\Engineering)
  • Databases with row- or column-level encryption
  • Document repositories (for example, SharePoint Online sites with CUI-specific permissions)

Draw Data Flows
Use arrows to connect external entities → processes → data stores → external entities, labeling each arrow with the type of CUI and transport method. Clearly denote when encryption or other controls apply (for example, “HTTPS TLS 1.2+” or “SFTP with AES-256”).

Overlay Security Controls
Annotate each process or data store with relevant NIST SP 800-171 security controls (for example, “Access Control – Role-based,” “Audit Logging Enabled,” or “Encrypted at Rest”).

Review and Validate
Circulate the draft diagram to stakeholders—including the security team, system administrators, and compliance personnel—to ensure no CUI flow is overlooked. Revise based on feedback.

Best Practices for Your CUI Data Flow Diagram

  • Keep It Simple Yet Comprehensive
    Avoid plotting every low-level server or workstation. Focus on systems and processes where CUI is genuinely in scope.
  • Use Standardized Symbols
    Stick to common DFD notation (circles or rounded rectangles for processes, open-ended rectangles for data stores, stick figures or rectangles for external entities).
  • Label Clearly
    Every arrow should specify the type of CUI and its classification level (for example, “Technical Data – CUI”). If encryption is applied, note it (for example, “Encrypted SFTP”).
  • Version and Date
    Maintain version control. As new applications come online or processes change, update the CUI data flow diagram promptly and record the revision date.
  • Integrate with System Security Plans (SSP)
    Many organizations include their DFD as an appendix in the SSP. This helps auditors cross-reference documented controls with actual data flows.
  • Automate Where Possible
    If your environment includes a configuration management database (CMDB) or security orchestration tools, leverage automated discovery to validate that CUI storage locations match what’s depicted in your DFD.

Example: Simplified CUI Data Flow

Below is a simplified illustration of a CUI data flow diagram for an organization that receives design specifications from a defense prime:

External Entity (Prime Contractor)
• Uploads CUI via a secure web portal (HTTPS/TLS 1.2+).

Process (Web Portal Server)
• Validates user credentials with multi-factor authentication.
• Stores received design specs temporarily in an encrypted staging directory.

Process (Automated Ingestion Script)
• Moves files from staging to the Document Management System (DMS) on a file server.

Data Store (Encrypted File Server)
• Houses CUI under \FileShare\Engineering\DesignSpec with access restricted to the Engineering AD group.
• All backups of this share are encrypted using AES-256.

Process (User Workstation)
• Authorized engineering staff access design specs via a mapped drive.
• Workstations have disk-level encryption and anti-malware enabled.

External Entity (Regulatory Audit Team)
• Retrieve audit logs from a logging server over a separate secure channel (SSH/SCP) to verify who accessed CUI.

Conclusion

A well-crafted CUI data flow diagram is more than a compliance checkbox. It serves as a blueprint for how your organization handles sensitive information. By clearly mapping external entities, processes, data stores, and data flows, you not only demonstrate adherence to NIST SP 800-171 and CMMC requirements but also gain invaluable insight into potential security gaps.

Whether you are preparing for a CMMC assessment or aiming to bolster your security posture, investing time in creating and maintaining a detailed CUI data flow diagram will pay dividends in reduced risk and smoother audits. Start by identifying all CUI touchpoints in your environment, leverage standardized DFD symbols, and ensure every flow is labeled with data classification and security controls. Keep the diagram current as systems evolve, and use it as a living artifact in your System Security Plan.

By following these guidelines, you will have a practical, actionable CUI data flow diagram that not only meets regulatory requirements but also strengthens your overall data protection strategy.