https://www.bleepingcomputer.com/news/security/recently-fixed-windows-zero-day-actively-exploited-since-mid-2020/

Microsoft says that a high-severity Windows zero-day vulnerability patched during the February 2021 Patch Tuesday was exploited in the wild since at least the summer of 2020 according to its telemetry data.

The actively exploited zero-day bug is tracked as 'CVE-2021-1732 - Windows Win32k Elevation of Privilege Vulnerability.'