CMMC Practice AC.1.003
Verify and control/limit connections to and use of external information systems.
Bold Coast Security Guidance
You may have external resources, such as cloud providers, which the organization utilizes and must be approved for use and managed.
Larger organizations may also implement internal controls which limit access to certain areas of your network to certain users/devices, but those will be better defined in other practices.
Your policies should state that the organization will verify and control/limit connections to, and use of, external information systems, and that only approved company devices are permitted access to company information systems and resources.
Your plan will note any steps taken to ensure only company devices are used on the network, such as making devices enroll in Active Directory and any approved cloud service provider, or other external resource. The organization will measure the effectiveness of the plan by periodic internal scans of the network for unauthorized devices and review of logs from proxy servers, filters, or other internet access monitoring systems.
DRAFT NIST SP 800-171 R2
External systems are systems or components of systems for which organizations typically have no direct supervision and authority over the application of security requirements and controls or the determination of the effectiveness of implemented controls on those systems. External systems include personally owned systems, components, or devices and privately-owned computing and communications devices resident in commercial or public facilities. This requirement also addresses the use of external systems for the processing, storage, or transmission of Federally Contracted Information, including accessing cloud services (e.g.,infrastructure as a service, platform as a service, or software as a service) from organizational systems.
Organizations establish terms and conditions for the use of external systems in accordance with organizational security policies and procedures. Terms and conditions address as a minimum, the types of applications that can be accessed on organizational systems from external systems. If terms and conditions with the owners of external systems cannot be established, organizations may impose restrictions on organizational personnel using those external systems.
This requirement recognizes that there are circumstances where individuals using external systems (e.g., contractors, coalition partners) need to access organizational systems. In those situations, organizations need confidence that the external systems contain the necessary controls so as not to compromise, damage, or otherwise harm organizational systems. Verification that the required controls have been effectively implemented can be achieved by third-party, independent assessments, attestations, or other means, depending on the assurance or confidence level required by organizations. Note that while “external” typically refers to outside of the organization’s direct supervision and authority, that is not always the case. Regarding the protection of Federally Contracted Information across an organization, the organization may have systems that process Federally Contracted Information and others that do not. And among the systems that process Federally Contracted Information there are likely access restrictions for Federally Contracted Information that apply between systems. Therefore, from the perspective of a given system, other systems within the organization may be considered “external" to that system.