What is the primary purpose of limiting the use of portable storage devices on external systems according to CMMC practice?

The primary purpose of limiting the use of portable storage devices on external systems is to protect Controlled Unclassified Information (CUI) from unauthorized access. CUI is sensitive information that, while not classified, still requires safeguarding to prevent data breaches and unauthorized disclosure. Portable storage devices, such as USB drives, can easily be lost, stolen, or infected with malware, leading to potential security vulnerabilities. By restricting their use, organizations mitigate the risk of CUI being accessed by unauthorized individuals or systems.

Focusing on this protective measure not only enhances the security posture of the organization but also aligns with the overall CMMC framework's objective of ensuring the confidentiality, integrity, and availability of sensitive information in compliance with relevant government regulations.