The Cybersecurity Maturity Model Certification (CMMC) framework is a new and evolving compliance standard for contractors working with agencies under the Department of Defense (DoD) or select Executive Branch functions.
Much of this framework focuses on the readiness of a contractor to manage risk and security in their IT systems, and the capabilities they have to handle Controlled Unclassified Information (CUI). Since this is such a new framework, however, there is a push to train cybersecurity auditors and managed service providers who can successfully audit contractors in the upcoming years. Accordingly, there are plenty of companies out there advertising that they can provide training for CMMC audits and implementation.
You must vet any organization that claims they can provide authorized instruction or assessments for CMMC authorization.