Infinite loop in Recurrence.GetNumberOfYearsBetween() with the Japanese calendar in Exchange Server 2019 and 2016

Symptoms

When there's a recurring calendar item based on Japanese Lunar calendar, Recurrence.GetNumberOfYearsBetween() can go into an infinite loop in Microsoft Exchange Server 2019 or Exchange Server 2016. This saturates CPU and makes EWS unusable for all users.

Resolution

To fix this issue, install one of the following updates:

• The Cumulative Update 3 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.
  

• The Cumulative Update 14 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.

References

Learn about the  terminology that Microsoft uses to describe software updates.