An elevation of privilege vulnerability exists in Dynamics On-Premise v9. An attacker who successfully exploited the vulnerability could leverage a customizer privilege within Dynamics to gain control of the Web Role hosting the Dynamics installation. To exploit this vulnerability, an attacker needs to have credentials for a user that has permission to author customized business rules in Dynamics, and persist XAML script in a way that causes it to be interpreted as code. The update addresses the vulnerability by restricting XAML activities to a whitelisted set.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1229