Executive Summary:
Cybersecurity Maturity Model Certification (CMMC) and National Institute of Standards and Technology Special Publication 800-171 (NIST SP 800-171) are closely related, but they are not interchangeable. Many defense contractors assume that implementing NIST 800-171 automatically satisfies CMMC requirements. In practice, CMMC builds on NIST 800-171 by formalizing how compliance is verified, enforced, and sustained over time. Understanding the difference is critical for contractors that want to remain contract-eligible as CMMC requirements begin appearing in Department of Defense solicitations.
What NIST SP 800-171 Is (and Isn’t)
NIST SP 800-171 defines 110 security controls designed to protect Controlled Unclassified Information (CUI) in non-federal systems. For years, contractors were required to implement these controls through Defense Federal Acquisition Regulation Supplement (DFARS) clause 252.204-7012, typically via self-attestation.
What NIST 800-171 does well is establish what safeguards must exist. It does not prescribe a standardized mechanism for third-party validation or a uniform enforcement model across the Defense Industrial Base.
This gap contributed to the creation of CMMC.
What CMMC Adds to the Equation
CMMC does not replace NIST SP 800-171. Instead, it operationalizes and enforces it.
For CMMC Level 2, the technical requirements are the same 110 controls outlined in NIST 800-171.
The difference is that compliance must be:
- Verified by a third party (a C3PAO for most contractors)
- Demonstrated through evidence, not just documented intent
- Sustained operationally, not addressed as a one-time exercise
CMMC introduces formal assessment methodologies such as Examine, Interview, and Test, which require organizations to prove that controls are implemented, understood by staff, and functioning as intended.
Where Contractors Commonly Get Tripped Up
The most common misunderstanding is believing that a written System Security Plan (SSP) or a past self-assessment equates to readiness. Under CMMC, assessors expect alignment between policies, technical configurations, and real-world outcomes.
Another frequent challenge is documentation quality. CMMC assessments scrutinize whether policies, procedures, SSP narratives, and system configurations tell the same story. Gaps between what is written and what is deployed are often what cause findings.
Finally, many organizations underestimate the organizational readiness component. Staff must be able to explain processes, demonstrate tools, and show consistent execution of security practices.
CMMC Is About Accountability, Not New Controls
A useful way to think about the relationship is this:
- NIST 800-171 defines the controls
- CMMC defines how compliance is proven
CMMC raises the bar by removing ambiguity around enforcement. It creates a standardized, auditable model that applies consistently across the Defense Industrial Base.
What This Means for Defense Contractors
If your organization handles CUI and plans to pursue Department of Defense contracts, NIST 800-171 implementation is no longer sufficient on its own. Contractors must prepare to demonstrate compliance under formal assessment conditions.
Those that treat CMMC as a documentation update often struggle. Those that treat it as an operational discipline, aligning people, processes, and technology, are far better positioned to pass assessments and remain competitive.
Resources that support CMMC compliance:
