An elevation of privilege vulnerability exists due to a stack corruption in Windows Subsystem for Linux. An attacker who successfully exploited the vulnerability could execute code with elevated permissions. To exploit the vulnerability, a locally authenticated attacker could run a specially crafted application. The security update addresses the vulnerability by correcting how Windows Subsystem for Linux handles objects in memory.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1185