If your organization handles Controlled Unclassified Information (CUI)—or expects to for a Department of Defense contract—chances are you’re working toward Cybersecurity Maturity Model Certification (CMMC) compliance. And that means you need to show not just that you have security controls, but that you track how sensitive information moves through your systems. This is where data flow diagrams (DFDs) come in.
Data flow diagrams are simple, visual roadmaps that show how information enters, moves through, and exits your organization. These aren’t just for IT teams—they’re essential for compliance officers, auditors, and anyone responsible for protecting sensitive data. DFDs help you spot weak points, make sure you’ve got the right security in the right places, and demonstrate that you know exactly where your CUI lives.
What Does a Data Flow Diagram Do?
A DFD uses basic shapes—circles for processes, rectangles for storage, and arrows to show direction—to map out the lifecycle of your data. This isn’t about hardware or network wires; it’s about what happens to the data itself. Where does it come in? Who touches it? Where does it go? If you’ve never built one before, don’t worry—they’re straightforward, and getting started is easier than you think.
With a DFD, you can quickly see if sensitive data is exposed in risky places or if there’s a step missing in your security. For example, if CUI arrives by email, does it go straight to a secure server, or does it pass through an insecure desktop first? These are the kinds of gaps that auditors look for—and that attackers exploit.
DFDs vs. Network Diagrams
It’s easy to mix up DFDs and network diagrams, but they’re different tools for different jobs. A network diagram shows you how your devices connect—your routers, switches, servers, and firewalls. A DFD, on the other hand, focuses on what happens to your data as it moves through those devices. Think of a network diagram as a map of your city’s roads, while a DFD shows you how mail (your data) travels from a sender to a recipient.
For CMMC, both matter, but if you’re handling CUI, the DFD is non-negotiable. It proves you’re not just running security software—you actually understand and control the movement of sensitive information.
How to Build a Data Flow Diagram
If you already have a network diagram, you’re halfway there. Here’s how to turn it into a DFD:
-
Find Your Entry Points: Identify every way CUI comes into your system—email, file uploads, USB drives, third-party portals, etc.
-
Map the Data’s Journey: Trace what happens to the data after it arrives. Does it get stored? Processed? Sent to another system? Each step gets its own symbol on your diagram.
-
Mark the Exit Points: Figure out where CUI leaves your network—exports, downloads, transfers to partners, etc. Each exit needs a clearly labeled endpoint.
-
Review and Refine: Go over your diagram with your IT and compliance teams. Double-check that nothing’s missing. Update it whenever your processes change.
Use clear, consistent symbols and labels. Keep your diagram simple—auditors shouldn’t need a decoder ring to understand it. And, most importantly, make sure it matches reality. Test it against actual data flows. If you find a gap, fix the diagram and the process.
Best Practices
-
Document Everything: Leave no process or storage location out. If data touches it, it should be on the diagram.
-
Standardize Your Symbols: Use the same shapes and terms throughout. Confusing diagrams lead to compliance headaches.
-
Collaborate: Get input from IT, security, compliance, and anyone else who handles sensitive data. Different perspectives catch different risks.
-
Keep It Fresh: Update your DFD whenever you change your network, add new software, or adjust your workflows. Outdated diagrams are worse than useless.
Common Pitfalls
A lot of organizations stumble with DFDs. Sometimes, they miss a data flow entirely. Other times, symbols and labels are inconsistent, or teams don’t communicate. The biggest mistake? Letting your diagram gather dust after you’ve built it.
Avoid these traps by auditing your actual data flows, standardizing your diagrams, and involving all the right people. Use your network diagrams as a starting point, but don’t stop there. Schedule regular reviews, and make updating your DFDs part of your change management process.
Why This Matters for Audits
CMMC auditors love DFDs. A clear, accurate diagram answers most of their questions at a glance: Where does CUI enter? Where does it go? How is it protected along the way? If your DFD is incomplete or confusing, expect a lot of follow-up—and possibly a failed audit.
Auditors might ask, “Can you show us how CUI travels through your network?” or “How do you secure entry points for sensitive data?” With a solid DFD, you can answer confidently and back up your compliance claims.
The Bottom Line
If you’re serious about CMMC, you need data flow diagrams—not as a checkbox, but as a living part of your cybersecurity practice. They’re your best defense against both cyber threats and compliance trouble. Take the time to build them right, keep them current, and use them to guide your security decisions.
If you want expert help—or just a second set of eyes—consider partnering with Intech Hawaii. We are focused on Security-First and specialize in CUI and CMMC. But don’t wait. The sooner you map your data flows, the sooner you’ll be ready for whatever comes next.
