Currently, the New-ExchangeCertificate cmdlet uses the SHA-256 hash algorithm instead of the less secure SHA-1. However, the automatic creation of a default self-signed authentication certificate that occurs during the Setup program calls a different code path than the path that's called by the cmdlet. This causes the program to issue certificates by using the SHA-1 hash algorithm.
To fix this issue, install one of the following updates:
Important: Our testing indicates that this fix works on only fresh installations. If you apply this fix on an upgraded installation, the program might continue to experience this issue.
Learn about the terminology that Microsoft uses to describe software updates.