Subcontractor's Guide to CMMC: Your Responsibilities Explained

Introduction: Why Subcontractors Cannot Ignore CMMC

If you are a subcontractor supporting the defense industrial base (DIB), you may have heard the phrase "CMMC requirements flow down." But what does that actually mean for your business, and what happens if you do not comply?

The Cybersecurity Maturity Model Certification (CMMC) program was created by the Department of Defense (DoD) to protect sensitive government information throughout the entire defense supply chain — including every subcontractor and vendor regardless of company size or revenue. This guide breaks down exactly what subcontractors need to know: your specific obligations, how scoping works, and the consequences of non-compliance.

1. What Is CMMC and Why Does It Apply to Subcontractors?

CMMC is a certification framework establishing cybersecurity requirements for any company doing business with the DoD. The program protects two key types of information:

Federal Contract Information (FCI): Information provided or generated under a government contract that is not intended for public release.

Controlled Unclassified Information (CUI): Sensitive but unclassified information that requires protection under federal law, regulation, or government-wide policy.

CMMC requirements are embedded in DoD contracts through the Defense Federal Acquisition Regulation Supplement (DFARS). When a prime contractor signs a DoD contract, they accept responsibility for ensuring their entire supply chain — including you — meets the cybersecurity requirements specified in that contract.

This is the flow-down requirement, and it is not optional. Prime contractors must verify that all subcontractors handling FCI or CUI meet the applicable CMMC level before those subcontractors can perform covered work.

2. How to Determine Your CMMC Level as a Subcontractor

Your required CMMC level is determined by the type of information you handle — not your company size, headcount, or revenue.

Most subcontractors fall into Level 1 or Level 2. The deciding factor is straightforward: if your work involves accessing, storing, processing, or transmitting CUI, you need Level 2 at minimum.

3. Understanding Scoping: What Systems Are Actually In or Out?

One of the most misunderstood parts of CMMC compliance for subcontractors is scoping — the process of defining which systems, people, and processes must actually meet CMMC requirements. Getting this wrong in either direction creates problems. Scope too broadly and you overspend. Scope too narrowly and you are out of compliance.

What Falls Within Scope?

The CMMC assessment scope includes all assets that process, store, or transmit CUI, plus the security tools that protect those assets. In practice this typically means:

• Systems and networks where CUI lives or travels
• Endpoints such as laptops, workstations, and servers used to access or work with CUI
• Security tools protecting those systems, including firewalls, endpoint protection, and identity management
• Cloud services where CUI is stored or processed
• Personnel with access to CUI

What Can Be Scoped Out?

Assets that do not touch CUI and are properly isolated from systems that do can potentially be excluded from scope. This is where a well-designed network segmentation strategy delivers real financial value. If you can clearly demonstrate that certain systems have no pathway to CUI, those systems may not need to meet CMMC controls.

The CUI Enclave Strategy

Many subcontractors reduce compliance costs by creating a CUI enclave — a tightly controlled, isolated environment where all CUI work happens. By confining CUI to this enclave, you limit what must meet CMMC requirements. This approach can significantly reduce both the cost and complexity of your compliance effort, and is worth discussing with a qualified RPO before you begin implementation.

4. Your Specific CMMC Obligations as a Subcontractor

If your subcontract flows down a CMMC level requirement, here is exactly what you are accountable for:

a) Achieve and Maintain Your Required CMMC Level

You must achieve certification before performing any work that involves CUI. For Level 2 contracts on critical programs, this means completing a third-party assessment by a Certified Third-Party Assessment Organization (C3PAO) and receiving a passing score. Certification is not a one-time event — it must be maintained and reaffirmed on a regular cycle.

b) Create and Maintain a System Security Plan (SSP)

You are required to document how your organization implements each applicable CMMC practice in a System Security Plan. This is a living document that must be kept accurate and up to date. An SSP that does not match your actual environment is a compliance violation in itself, even if your controls are technically in place.

c) Manage a Plan of Action and Milestones (POA&M)

For any controls not yet fully implemented, you need a POA&M documenting what is missing, why, and your concrete plan to close the gap. For Level 2 contracts requiring a C3PAO assessment, certain critical controls must be fully implemented. Open POA&M items on those controls will result in a failed assessment.

d) Submit Your Score to SPRS

Subcontractors handling FCI are required to post their self-assessment score in the DoD Supplier Performance Risk System (SPRS). This score must be updated annually and whenever significant changes to your environment occur. Falsely affirming compliance in SPRS carries serious legal exposure under the False Claims Act.

e) Report Cybersecurity Incidents Within 72 Hours

If a cybersecurity incident occurs on your systems that affects or potentially affects CUI, you are required to report it to the DoD within 72 hours via the DIBNet portal. You must also preserve all potentially relevant system images and data for at least 90 days to support any DoD investigation that follows.

5. What Happens If a Subcontractor Is Not CMMC Compliant?

Non-compliance carries real business and legal consequences. This is not a situation where you can fall a little short and negotiate your way through it.

6. What to Do If You Do Not Know Your Compliance Status

If you are unsure where you stand, you are in good company. Many subcontractors have been performing defense work for years without a clear picture of their CMMC readiness. The important thing is to start now, before a contract deadline forces the issue.

Step 1: Identify your CUI.
Map where CUI enters your organization, where it is stored, and who touches it.

Step 2: Define your scope.
Determine which systems are in scope based on your CUI data flows.

Step 3: Perform a gap assessment.
Compare your current security controls against the required CMMC practices.

Step 4: Build a remediation plan.
Prioritize the gaps and create a realistic timeline to close them.

Step 5: Work with a CMMC RPO.
A Registered Practitioner Organization can guide you through assessment prep, implementation, and documentation.

7. How CISPOINT Helps Subcontractors Achieve CMMC Compliance

CISPOINT is a Cyber-AB Registered Practitioner Organization (RPO) based in the DMV area, with clients across Maryland, Virginia, Alabama, Kentucky, and Florida. We specialize in right-sizing CMMC compliance for small and mid-sized subcontractors who need a practical, cost-effective path to certification without paying for controls they do not need.

Our subcontractor services include:

• CUI identification and data flow mapping
• CMMC scoping and CUI enclave design
• Gap assessments against NIST SP 800-171 and CMMC Level 2 requirements
• System Security Plan (SSP) development and maintenance
• Plan of Action and Milestones (POA&M) creation and remediation tracking
• Fully managed and co-managed IT services to implement required controls
• SPRS score calculation and submission support
• Assessment preparation for C3PAO evaluations

Whether you are just beginning to understand your obligations or facing an assessment deadline, CISPOINT helps you build a compliant, defensible environment without overspending.

Frequently Asked Questions

Q: I am a very small subcontractor. Do CMMC requirements still apply to me?

Yes. CMMC applies based on the type of information you handle, not your company size. If you touch CUI as part of your defense work, you must comply. That said, a qualified RPO can help small businesses find the most efficient and cost-appropriate compliance path.

Q: My prime contractor has not asked me about CMMC yet. Am I in the clear?

Not necessarily. CMMC is being phased into DoD contracts over several years. The fact that your prime has not asked yet does not mean the requirement is not coming. It almost certainly is. Getting ahead of it is always better than scrambling when a contract deadline arrives.

Q: Can I use a managed service provider to help me meet CMMC requirements?

Yes, and for many subcontractors this is the most cost-effective approach. An MSP experienced in CMMC can implement and manage required controls as a service rather than requiring you to build an in-house security team. Keep in mind that MSP systems touching your CUI become part of your assessment scope — so choose an MSP with documented CMMC experience.

Q: What is the difference between a self-assessment and a C3PAO assessment?

A self-assessment means your own team evaluates your compliance and submits the score in SPRS. A C3PAO assessment is conducted by an independent, DoD-authorized Certified Third-Party Assessment Organization. Level 2 contracts for critical programs require a C3PAO assessment. Level 1 and some Level 2 contracts allow self-assessment.

Q: How long does it take to become CMMC compliant as a subcontractor?

It depends on your starting point. Organizations with solid existing security controls may achieve compliance in 3 to 6 months. Those building from the ground up should plan for 9 to 18 months, especially when significant infrastructure changes are needed. Starting early is critical — waiting until an assessment deadline is imminent leaves almost no margin to address gaps.