Microsoft is bundling Intel microcode (BIOS) updates meant to fix the graver version of the Spectre vulnerability as Windows Update packages made available via the Microsoft Update Catalog portal. Microsoft did not initially plan to distribute microcode updates at the software level, and deferred the patching operations to OEMs. The OS maker later changed its mind because some OEMs were missing in action, failing to integrate Intel’s microcode fixes. Microsoft is embedding these Intel CPU microcode patches as updates to the operating system’s CPU driver.
Source: https://www.bleepingcomputer.com/news/microsoft/a-bunch-of-intel-microcode-patches-have-arrived-on-the-microsoft-update-catalog/