Closing the CMMC Grey Space: Why Vendor Capabilities Do Not Equal Compliance Outcomes

(This is Part II in our series on CMMC compliance for organizations serving defense contractors. Part I introduced the three pillars framework, showing how vendor capabilities, organizational implementation, and C3PAO validation must align for certification success. This article examines the operational gap where that alignment most commonly fails)

The “grey space” – the gap between vendor capabilities and organizational evidence – causes more CMMC failures than missing security controls. This article focuses on the operational gap and provides the framework to close it.

The Grey Space Problem
As for federal compliance programs I have supported, the pattern is consistent. Organizations invest in platforms marketed as “CMMC-ready,” assume compliance follows, and discover during assessment that they have purchased only the potential for compliance.

Consider a common scenario:
A managed service provider deploys multifactor authentication to address IA.L2-3.5.3 (use multifactor authentication for local and network access to privileged accounts). Users authenticate with MFA daily. The technology functions as intended. On paper, the requirement appears to be satisfied.

During the C3PAO assessment, the control is marked Not Met.

The failure is not technical. The organization enforced MFA within the customer’s Microsoft 365 tenant but did not enforce MFA on its own remote monitoring and management platform. That platform operates with SYSTEM-level privileges across managed endpoints. A technician accessing the RMM console without MFA introduces an unprotected privileged access path.

The vendor provided the MFA capability for both environments, but the organization only implemented it in one of them. As a result, the control failed in the grey space.

Shared Responsibility Is Architectural, Not Conceptual

CMMC Level 2 aligns with NIST Special Publication 800-171 Revision 2, which defines 110 security requirements across 14 control families. (Note: NIST published Revision 3 in May 2024 with updated control language; however, CMMC requirements remain mapped to revision 2 pending DoD transition guidance).

When third-party platforms are introduced, responsibility for these requirements is distributed across three distinct categories.

1. Inherited controls are implemented entirely by the vendor. Customers cannot alter their technical operation. Cryptographic modules used by a backup provider are a typical example. If the vendor uses NIST-validated cryptography, the customer inherits that control. If the vendor does not, the customer cannot remediate the gap through policy or configuration.
2. Shared controls require action from both parties. The vendor supplies the mechanism; the customer defines how it is configured and used. Patch management illustrates this clearly. The platform provides deployment, scheduling, and reporting capabilities. The customer determines scope, timing, exception handling, and review cadence. Both parties must fulfill their respective responsibilities for the control to be met.
3. Customer-managed controls remain entirely the customer’s responsibility. Vendors may provide supporting tools, but implementation rests solely with the organization. Physical security of staff workspaces falls into this category, regardless of how extensively remote access tools are used.

The grey space emerges primarily within shared controls, where responsibility boundaries are poorly defined, misunderstood, or insufficiently documented.

The Shared Responsibility Matrix as a Translation Layer

The primary mechanism for defining these boundaries is the Shared Responsibility Matrix (SRM). A functional SRM translates NIST 800-171 requirements into explicit, testable obligations for both vendor and customer.

What distinguishes a usable SRM from a liability disclaimer is precision. A credible SRM maps responsibility to specific control identifiers, not broad or generic statements. It assigns actions clearly. One party generates logs. The other reviews them. One provides cryptographic modules while the other enables approved configurations.

Configuration requirements must be explicit. If a platform includes FIPS-validated cryptography but ships with FIPS mode disabled, the SRM should clearly state that activation is required. Evidence responsibilities must also be unambiguous. Vendor attestations alone are insufficient. Customers must understand which artifacts they are expected to generate and retain.

Common warning signs in vendor SRMs include:

• Assertions that security is “shared” without assigning specific responsibility
• Partial coverage addressing only a subset of NIST 800-171 controls
• References to external documentation in place of clear responsibility statements
• Blanket disclaimers that shift all accountability to the customer

A defensible SRM maps all applicable controls and clearly defines vendor and customer ownership, obligations, and expectations.

Inherited Controls Still Require Action

Inherited controls still require the organization to verify their implementation, formally document the inheritance, and maintain ongoing oversight to satisfy C3PAO expectations.

Consider SC.L2-3.13.8, which requires cryptographic mechanisms to protect Controlled Unclassified Information (CUI) in transit. If a backup vendor uses NIST-validated cryptography, the customer inherits the cryptographic implementation itself. The customer cannot alter cipher suites or key exchange mechanisms. However, inheritance does not eliminate responsibility. The customer must verify, enable, and document that inheritance.

Verification requires obtaining the vendor’s Cryptographic Module Validation Program certificate and confirming that its scope covers the cryptographic functions in use. Configuration requires ensuring that approved modes are enabled and that non-compliant fallback options are disabled. Documentation requires explicitly referencing the vendor’s implementation within the System Security Plan and tying it to deployed configurations.

Without these steps, inherited controls frequently fail during assessment—not because the technology is inadequate, but because oversight and documentation are incomplete.

What C3PAOs Actually Evaluate

C3PAO assessments rely on three methods: examination of documentation, interviews with personnel, and technical testing. Grey space failures occur when these methods produce inconsistent or conflicting results.

Documentation may state that logs are reviewed weekly. Interviews may reveal that staff assume automated tools handle review. Technical testing may show that reports are generated but never analyzed. In that case, the control fails – not because logging technology is absent, but because responsibility for review and response was never clearly assigned or operationalized.

The gap between automation and human accountability is one of the most common sources of Level 2 findings.

Turning Capabilities into Controls

Closing the grey space requires explicit mapping of responsibilities and evidence. The table below illustrates how to translate platform features into assessable controls.

Platforms that successfully support CMMC assessments are not distinguished by the number of controls they claim to cover, but by how clearly they separate vendor capability from organizational responsibility. In Ncentral, controls are treated as operational systems designed to generate assessable evidence, but only when paired with defined organizational action, as reflected in the platform’s SRM and supporting documentation.

Closing the Grey Space

CMMC Phase 2 enforcement begins November 10, 2026. Time pressure is real, but speed does not close compliance gaps – clarity does.

Organizations should obtain SRMs from every critical vendor, map all 110 NIST 800-171 requirements, and identify where responsibility is undefined or ambiguous. Those gaps represent an assessment of risk.

The work that follows is operational. Configure systems to generate evidence by default. Define review responsibilities explicitly. Ensure that documentation, personnel understanding, and technical reality align.

Compliance outcomes are not created by better tools alone. They are achieved through clearly defined responsibility boundaries, documented execution, and sustained evidence.

Start with your Endpoint Management. Request their SRMs. If they cannot provide one, or if their matrix covers only a small subset of applicable controls, you have identified a grey‑space risk that operational discipline alone cannot resolve.

Next Steps:

Download the N‑central Shared Responsibility Matrix from the N‑able today to identify your Grey Space risks before the assessor does.