A Supplement to NIST Special Publication 800-171 – The requirements for enhanced security capabilities that address high end threats, as identified and selected by a federal agency, are in addition to the basic and derived requirements in NIST SP 800-171. This publication provides federal agencies with recommended enhanced security requirements for protecting the confidentiality of CUI:

(1) when the information is resident in nonfederal systems and organizations;

(2) when the nonfederal organization is not collecting or maintaining information on behalf of a federal agency or using or operating a system on behalf of an agency; and

(3) where there are no specific safeguarding requirements for protecting the confidentiality of CUI prescribed by the authorizing law, regulation, or government-wide policy for the CUI category listed in the CUI Registry.

The enhanced requirements apply only to components of nonfederal systems that process, store, or transmit CUI or that provide security protection for such components when the designated CUI is associated with a critical program or high value asset.

The enhanced requirements supplement the basic and derived security requirements in NIST Special Publication 800-171 and are intended for use by federal agencies in contractual vehicles or other agreements established between those agencies and nonfederal organizations.

https://csrc.nist.gov/publications/detail/sp/800-172/draft