With respect to legacy systems, What RMF Steps can be applied to validate the security categorization to ensure appropriate security controls have been selected and implemented. Response:

When dealing with legacy systems, reapplying RMF Steps 1 (Categorize), 2 (Select), and 3 (Implement) is effectively conducting a gap analysis. This process helps determine if the existing security categorization is still valid and if the appropriate security controls have been adequately selected and implemented for the current operational environment.

RMF Steps 4-6 (Assess, Authorize, Monitor) occur after controls are selected and implemented; they are for evaluating and continuously managing the security posture, not for validating initial categorization or control selection.

Steps 4-6 are related to assessment and authorization, not primarily for validating categorization or control selection, and the primary analysis for existing controls in these initial steps would be a gap analysis, not an impact analysis.

While Steps 1-3 are correct, describing this re-application for validating selected and implemented controls as primarily an "impact analysis" is less precise than a "gap analysis," which specifically identifies discrepancies between required and existing controls.