AC-20 Use of external systems
What the standard requires
a. [establish [terms and conditions] | identify [controls asserted] ] , consistent with the trust relationships established with other organizations owning, operating, and/or maintaining external systems, allowing authorized individuals to: 1. Access the system from external systems; and 2. Process, store, or transmit organization-controlled information using external systems; or b. Prohibit the use of [prohibited types of external systems].
Quoted verbatim from NIST SP 800-53 Rev 5 (OSCAL catalog), which is in the public domain.
Cross-framework mappings
No cross-framework mapping is seeded for this control. That is stated rather than filled in: a mapping nobody authored is worse than a gap you can see.
In CMDash this control is a row with an owner, a status, uploaded evidence kept with its full history, and an export an assessor can read.