Working with the U.S. military or its private defense partners requires strict security controls to protect sensitive information. These expectations apply not only to defense contractors but also to the external service providers that support their systems and operations. To maintain CMMC compliance, organizations must account for all infrastructure that stores, processes, or transmits Controlled Unclassified Information (CUI), including assets managed by third parties.
Is your organization prepared to meet CMMC requirements across both internal systems and external service provider environments?
A CMMC-aligned advisory approach can help clarify shared responsibilities, reduce compliance gaps, and improve overall readiness.
CMMC Compliance and External Service Providers
The Cybersecurity Maturity Model Certification (CMMC) is a regulatory framework designed to protect sensitive data across the U.S. defense industrial base (DIB). It applies directly to contractors and subcontractors that work with the U.S. Department of Defense (DoD), and plays a critical role in establishing consistent cybersecurity standards.
For organizations pursuing CMMC compliance, securing internal systems alone is not enough. Third-party infrastructure, such as managed service providers, cloud platforms, and IT vendors, can also fall within the scope of CMMC when they store, process, or transmit Controlled Unclassified Information (CUI).
Despite this, the way CMMC requirements apply to external service providers is often misunderstood. Much of the discussion around the framework focuses on prime contractors, leaving organizations uncertain about how third-party relationships affect compliance obligations.
Understanding the impact of CMMC on external service providers requires clarity on:
- What the CMMC framework is and who it applies to directly
- Which third parties may be subject to CMMC requirements indirectly
- How organizations can align internal systems and external providers to achieve compliance
Working with a CMMC advisory partner can help organizations interpret requirements accurately, define shared responsibilities, and prepare for compliance across both internal environments and third-party services.
What Is CMMC, and Who Needs to Comply?
The Cybersecurity Maturity Model Certification (CMMC) program was created to reduce risk to sensitive government data across the Defense Industrial Base (DIB). It applies to public and private organizations that work with the U.S. Department of Defense (DoD) and handle Federal Contract Information (FCI) or Controlled Unclassified Information (CUI).
These two data types define the scope of CMMC compliance. Any organization that stores, processes, or transmits FCI or CUI as part of a DoD contract is subject to CMMC requirements.
At a high level, CMMC applies to most contractors and subcontractors with any exposure to FCI or CUI. However, the extent of compliance required depends on several factors.
CMMC is a tiered framework with three levels, each designed to address different risk profiles and data sensitivity. The required level is determined by:
- The type of information handled (FCI or CUI)
- The organization’s role within the DoD supply chain
- The level of risk associated with the environment
As discussed below, the CMMC level a contractor must achieve also affects whether external service providers fall within scope, and how much of the framework they must meet to support compliant operations.
What Counts as Contact with FCI or CUI?
CMMC’s applicability is determined less by the type of organization and more by how it handles protected data. To understand compliance obligations, it is essential to define Federal Contract Information (FCI) and Controlled Unclassified Information (CUI):
- Federal Contract Information (FCI) : Any information related to government contracts for services or products that is not intended for public release.
- Controlled Unclassified Information (CUI) : Information created or managed by the government that requires agency-specific protections. Examples include documentation on defense systems, nuclear programs, environmental data, and other sensitive capabilities.
For military contractors, any interaction with FCI or CUI : such as sending, receiving, storing, or processing a document—typically triggers CMMC compliance requirements.
For external service providers, compliance obligations depend on:
- The degree to which their systems or services come into contact with FCI or CUI
- The CMMC level required for the associated contract
Understanding these factors is critical for identifying which third parties must adhere to CMMC standards and at what level.
Are Third Parties In-Scope for CMMC Compliance?
While CMMC primarily applies to contractors working directly with the U.S. Department of Defense (DoD), compliance obligations often extend to third-party infrastructure and service providers that handle sensitive data on behalf of these contractors. Organizations seeking CMMC compliance must ensure that both internal systems and any third-party-managed assets adhere to the required cybersecurity standards.
Many individuals in the Defense Industrial Base (DIB) remain unclear about the full scope of CMMC requirements for third parties. For example, a 2025 LinkedIn post from a cybersecurity leader highlighted that even contractors fully aware of their responsibilities under CMMC Level 2 are frequently surprised when compliance obligations extend to subcontractors and external service providers (ESPs).
To close this gap, it is critical to understand which third parties are in scope and how CMMC requirements apply beyond the prime contractor:
- Subcontractors : Entities that provide goods or services supporting the prime contractor’s DoD obligations.
- External Service Providers (ESPs) : Vendors offering IT, cloud, managed, or other services that interact with systems containing FCI or CUI.
By identifying these parties and clarifying their compliance responsibilities, organizations can better manage risk and meet the expectations of DoD contracts.
Subcontractors’ CMMC Responsibilities
Under CMMC compliance, the definition of a subcontractor comes from the Code of Federal Regulations (CFR). Specifically, 48 CFR 3.502-1 defines subcontractors as entities that directly provide supplies, materials, equipment, or services to a military contractor in support of the prime contractor’s contractual obligations. In practical terms, these are third parties whose services are directly connected to an organization’s CMMC-related operations.
Whenever FCI or CUI comes into contact with a subcontractor, that subcontractor assumes corresponding CMMC compliance responsibilities. These responsibilities generally mirror the CMMC Level required of the prime contractor. For example, if a prime contractor is operating at Level 1 and conducts a self-assessment, any subcontractors handling FCI must meet the same assessment standards.
Another key consideration is contract language. Organizations seeking compliance must include clauses in subcontractor agreements that outline FCI and/or CUI safeguarding responsibilities, ensuring accountability and adherence to CMMC requirements.
External Service Providers’ CMMC Responsibilities
For CMMC compliance, the formal definition of an External Service Provider (ESP) comes from the Code of Federal Regulations. Specifically, 32 CFR 170.4(b) defines ESPs as external entities that an organization seeking compliance (OSC) utilizes for the provision and management of IT and/or cybersecurity services. An ESP is considered in scope only if CUI or Security Protection Data (SPD) touches the ESP’s resources, which triggers CMMC obligations.
In practice, this means CMMC responsibilities for ESPs are relevant primarily for Levels 2 and 3, where CUI is involved. Services that may involve CUI include cloud infrastructure, managed IT assets, security configurations, and ongoing IT oversight.
ESPs have two main compliance obligations under CMMC:
- Implement CMMC protections aligned with the Level required for their client’s CUI (Level 2 or 3).
- Provide documentation to clients, including Service Descriptions and a Customer Responsibility Matrix (CRM), which clearly delineates accountability for specific CMMC controls.
By adhering to these responsibilities, ESPs support their clients’ compliance efforts while ensuring that CUI is safeguarded across third-party-managed systems.
How to Achieve CMMC Compliance for All Parties
Achieving CMMC compliance across the Defense Industrial Base (DIB) requires familiarity, audit-readiness, and proactive management of CMMC controls.
For organizations seeking compliance (OSCs), this means understanding both internal obligations and third-party responsibilities. Contractors must ensure that subcontractors and external service providers (ESPs) meet CMMC requirements; failure to do so can jeopardize compliance and put lucrative DoD contracts at risk.
For third parties, including managed service providers (MSPs), achieving compliance means committing to security, transparency, and shared responsibility. Third-party organizations should be prepared to educate clients on their roles in protecting Federal Contract Information (FCI) and Controlled Unclassified Information (CUI) and to implement the necessary controls to meet the client’s CMMC Level.
As noted in a 2025 LinkedIn post from a cybersecurity expert, MSPs serving the defense sector must make a deliberate decision: either become CMMC-ready, equipped with Service Descriptions and a Customer Responsibility Matrix (CRM), or risk not meeting client expectations.
RSI Security provides CMMC advisory and readiness services, supporting organizations in understanding requirements and preparing for audits. This article is intended to guide preparation and awareness and does not constitute a formal certification determination.
CMMC Compliance Assessment Requirements
Any organization subject to CMMC compliance must implement the appropriate cybersecurity safeguards and understand the assessment requirements associated with their certification Level. Each Level has specific obligations for controls, audits, and verification, ranging from self-assessments to government-led certification audits.
- Implement 15 security controls derived from NIST SP 800-171 and aligned with FAR 52.204-21
- Conduct an annual self-assessment and affirmation
- Implement 110 controls, encompassing all of NIST SP 800-171
- Some Level 2 organizations qualify for self-assessment (pending DoD approval), while others require third-party audits
- All Level 2 assessments are conducted triennially, with annual affirmation
- Implement 134 controls, including all of NIST SP 800-171 plus 24 controls adapted from NIST SP 800-172
- Triennial certification assessments are led by government entities, with annual affirmation
For Level 2 assessments, third-party evaluations must be conducted by a Certified Third-Party Assessment Organization (C3PAO), vetted and listed by the Cyber AB. Level 3 certification audits are conducted by the Defense Industrial Base Cybersecurity Assessment Center (DIBCAC).
To streamline preparation and reduce compliance gaps, many organizations engage a CMMC advisory partner. Advisors help interpret assessment requirements, align responsibilities across internal and third-party systems, and ensure readiness for formal audits.
Streamline Your CMMC Compliance Processes
CMMC compliance remains relatively new, with full enforcement of the latest edition effective as of November 2025. Many organizations are still adjusting to what full compliance entails, for themselves and for their third-party partners. As enforcement timelines advance, military contractors and external service providers are reassessing their readiness and third-party dependencies.
RSI Security has supported numerous organizations across the Defense Industrial Base (DIB) in preparing for CMMC compliance. Our experience shows that a structured, advisory-driven approach is the most effective way to protect sensitive data and ensure readiness for audits.
To learn more about RSI Security’s CMMC advisory and readiness services, contact us today to discuss how your organization can achieve compliance with confidence.
