SC-2 — Separation of System and User Functionality

From control text to operational evidence

Use Separation of System and User Functionality as a testable risk decision. Translate the official statement into accountable people, repeatable processes, configured technology, and evidence that demonstrates the outcome over time. In this family, pay particular attention to secure architecture, boundary protection, communications protection, cryptography, and system isolation.

Implementation workflow

• Define the control boundary, responsible owner, inherited portions, and systems or processes in scope.
• Resolve each organization-defined parameter before declaring the control implemented.
• Document how the implementation satisfies every clause of the official control statement.
• Collect evidence as a normal byproduct of operation rather than only before an assessment.
• Review exceptions, changes, and monitoring results on a risk-based cadence.

Evidence examples

• network and trust-boundary diagrams
• firewall and gateway configurations
• cryptographic configuration and key records
• segmentation and isolation test results

Common failure patterns

• diagrams omit cloud and third-party paths
• encryption enabled without key governance
• flat trust zones allow unnecessary lateral movement
• boundary rules accumulate without owner review

Questions practitioners should ask

• What risk decision is this control intended to support in this system?
• Which parts are implemented locally, inherited, shared, or not applicable—and what evidence supports that decision?
• Do the documented narrative, deployed configuration, operating process, and collected evidence agree?
• What event or threshold requires the implementation to be reviewed or changed?