A security feature bypass vulnerability exists when Windows Secure Kernel Mode fails to properly handle objects in memory. To exploit the vulnerability, a locally-authenticated attacker could attempt to run a specially crafted application on a targeted system. An attacker who successfully exploited the vulnerability could violate virtual trust levels (VTL). The update addresses the vulnerability by correcting how Windows Secure Kernel Mode handles objects in memory to properly enforce VTLs.
https://www.tenable.com/blog/tenable-roundup-for-microsofts-june-2019-patch-tuesday
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1044
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2019-1044