There are three major improvements to this cumulative update, one of which fixes a side channel vulnerability recently discovered by Intel.MicrosoftExplain:
For 64-bit (x64) versionWindowsThe system provides protection against the speculative side channel vulnerability subclass, also known as microarchitecture data sampling (CVE-2019-11091, CVE-2018-12126, CVE-2018-12127, CVE-2018-12130). Use the registry settings described in the Windows client and Windows Server articles. (This registry setting is enabled by default in Windows client versions and Windows Server OS versions).
In addition, Microsoft said the update addresses bugs that affect Internet Explorer performance and corrupts text, layout, and cell size errors in Microsoft Excel when using certain fonts.
In the official support document, Microsoft only listed a known issue, warning that after installing this cumulative update, launching Windows Defender Application Guard or Windows Sandbox may fail with error 0x800705b4. The temporary workaround is to create a dedicated registry key.Instructions are provided here.