Microsoft has fixed 55 vulnerabilities, with four classified as Critical, 50 as Important, and one as Moderate. The three zero-day vulnerabilities patched today were publicly disclosed but not known to be used in attacks. Microsoft Exchange vulnerability was used by in the 2021 Pwn2Own hacking challenge. Other vendors who released updates in May include: Microsoft Exchange, Devcore, Team Viettel, Microsoft, Microsoft and others. None of today’s zero-days are known to have been actively exploited in the wild.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-may-2021-patch-tuesday-fixes-55-flaws-3-zero-days/