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CMMC Data Flow Diagrams Done Right: A CCA’s Perspective 

Bob Stephens
Best Practices Blog

Creating a Data Flow Diagram (DFD) is a foundational step in achieving Cybersecurity Maturity Model Certification (CMMC) compliance. DFDs offer a visual representation of how Controlled Unclassified Information (CUI) traverses through an organization’s systems. 

The process of identifying how FCI and CUI traverse an organization also highlights the people, processes, and technology that come in contact with FCI and/or CUI in the normal course of business—from finding, bidding on, and winning work, scoping the work, and delivering and invoicing for the work.  


Do You Need a Data Flow Diagram?

Having a DFD included in your organization’s CMMC documentation is critical. If the NIST 800-171 Controls represent how we protect CUI and FCI, the DFD (and the process used to create it) provides us a reliable means to determine “what” we are protecting, i.e., the FCI/CUI, and the people, processes, and technology that come in contact with this type of information. 

The DFD is not the same as a Network diagram. A Network diagram shows the network and devices on the network, whereas the DFD illustrates how the data (any data, but in this case FCI and CUI specifically) flows through the network and the devices on the network. 

Understanding the Importance of Data Flow Diagrams in CMMC 

DFDs are instrumental in: 

  • Identifying Authorization Boundaries: They help delineate the scope of people, systems, and processes that handle CUI (the ‘In Scope Assets’), which is crucial for defining the assessment boundaries as per CMMC requirements.   
  • Enhancing Security Posture: By mapping data flows, organizations can pinpoint areas where CUI might be at risk, allowing for the implementation of targeted security measures. Controls protect information and systems “in context” and understanding the state of the information (i.e., at rest, in transit, in processing) provides the context of how the control should be implemented. 
  • Facilitating Compliance Assessments: DFDs provide assessors with a clear understanding of data movements within the organization, streamlining the evaluation process. A visual reference to what is being protected (e.g., the CUI and the systems that store, process, and transmit it) helps an assessor understand the context of how the organization is protecting those assets. 

Certified CMMC Assessors have a unique perspective blending both advisory knowledge and a deep understanding of CMMC requirements. Taking this into account, we’ve put together a quick guide on what steps and how to take them to create an effective data flow diagram for CMMC. 

  1. Identify Data Entry Points: Determine where and how CUI enters your systems. This could be through email, web portals, or manual data entry. Thinking through how the organization does business can make this process easier by simply documenting all the steps a typical contract takes from ‘book to bill’.  
  1. Map Internal Data Movements: Chart the flow of CUI within your organization, noting how it’s processed, stored, and accessed by various systems and personnel.  
  1. Determine Data Exit Points: Identify where and how CUI leaves your systems, whether through reports, data exports, or transmissions to external entities. 
  1. Define System Components: List all hardware, software, and personnel involved in handling CUI. This includes servers, databases, applications, and user roles.  
  1. Establish System (Authorization) Boundaries: Clearly demarcate the systems and processes that fall within the scope of CMMC assessment. This helps in focusing security efforts and compliance checks. Visually, this is depicted as a ‘box’ around the in-scope systems and system components. 
  1. Review and Update Regularly: As systems evolve, ensure that your DFDs are updated to reflect any changes in data flows or system components. Note that major changes to the scope or boundary may require/necessitate an additional 3rd party assessment. 

Best Practices for Data Flow Diagrams in CMMC Compliance 

While there’s no set of rules for approaching a Data Flow Diagram, we’ve found successful implementations have had a few things in common: 

  • Simplicity and Clarity: Ensure that the DFD is easy to understand, avoiding unnecessary complexity. 
  • Ensure the scope covers both the boundary and internal flow: The boundary defines what’s in and out of scope, and the flow highlights the people, processes, and systems interacting with CUI. 
  • Use Standard Symbols: Adopt universally recognized symbols for processes, data stores, and data flows to maintain consistency. 
  • Incorporate Security Controls: Annotate the DFD with existing security measures in place at various points in the data flow. 
  • Engage Stakeholders: Collaborate with IT, security teams, and other relevant departments to ensure accuracy and comprehensiveness. 

Conclusion 

Developing a comprehensive Data Flow Diagram is a critical component in the journey toward CMMC compliance. It not only aids in identifying and mitigating potential security risks but also serves as a valuable tool during compliance assessments. By following the outlined steps and best practices, organizations can ensure that they have a clear understanding of how CUI is handled within their systems, paving the way for robust cybersecurity measures and successful certification.