A denial of service vulnerability exists when Microsoft Hyper-V Network Switch on a host server fails to properly validate input from a privileged user on a guest operating system. An attacker who successfully exploited the vulnerability could cause the host server to crash. To exploit the vulnerability, an attacker who already has a privileged account on a guest operating system, running as a virtual machine, could run a specially crafted application that causes a host machine to crash. The update addresses the vulnerability by modifying how virtual machines access the Hyper-V Network Switch.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0723