What is the difference between CMMC and NIST SP 800-171?

In practice, the primary distinction lies in the verification mechanism. NIST SP 800-171 compliance traditionally relies on self-attestation, where organisations develop a System Security Plan (SSP) and a Plan of Action and Milestones (POA&M) to document their implementation and any deficiencies. While this requires due diligence, it lacks independent validation. CMMC, conversely, mandates third-party assessments by CMMC Third-Party Assessment Organisations (C3PAOs) for Level 2, which directly maps to the NIST SP 800-171 requirements. This shift from self-attestation to external, verifiable assessment significantly impacts resource allocation, audit readiness, and the overall cybersecurity governance model for DIB contractors.

Furthermore, CMMC introduces a tiered maturity model, extending beyond the singular focus of NIST SP 800-171. While NIST SP 800-171 outlines 110 security requirements for CUI protection, CMMC v2.0 organises these into three levels: Level 1 (Foundational, for Federal Contract Information), Level 2 (Advanced, for CUI, directly aligning with NIST SP 800-171), and Level 3 (Expert, for CUI on critical programmes, based on NIST SP 800-172). This tiered approach allows the Department of Defense to specify the required cybersecurity maturity based on the sensitivity of information handled, thereby providing a more granular and enforceable framework for supply chain security.