A vulnerability in Windows 10 Update Assistant enables malicious users to run code with SYSTEM permissions.
The elevation of privilege is documented in CVE-2019-1378, where Microsoft explains that an attacker can create a full user account by eventually gaining access to install malware to take control of the device.
"There is a privilege vulnerability in Windows 10 Update Assistant in the way it manages permissions", says Microsoft.
“A locally certified intruder could run malicious code with increased system privileges. After successfully exploiting the vulnerability, the attacker could install programs, view, change, or delete data, create new accounts with full user rights. "
The bug was discovered and reported to Microsoft by Jimmy Bayne and is available in Windows 10 Update Assistant regardless of the version of Windows 10 you have installed.
As mentioned in Bleepingcomputer, some computers start running Windows 10 Update Assistant after the KB4023814 update is installed. However, this update is only for devices running Windows 10 in the 1803 version (April 2018 Update) or later and is supposed to prepare the "ground" for upgrading to Windows 10 to the 1903 version (May 2019 Update).
On the other hand, devices running Update Assistant on Windows 10 on the 1903 version are also vulnerable to attacks if the update was installed manually.
Microsoft has already released a new version of Update Assistant to resolve the vulnerability and recommends all users to install it as soon as possible. The only way to fix the bug is to manually install this new version, at least until the patch is included in some bug fixes. Of course you should uninstall the older version:
Microsoft reports that the defect was not publicly disclosed and thus no (yet) exploit has been released. However, you need to update your system.