The update with the number KB3062157 fixes a critical vulnerability in Exchange 2013 CU8 and SP1, which makes it possible to gain higher permissions. other versions are apparently not affected. More information can be found here:
https://technet.microsoft.com/library/security/MS15-064
It is not necessary to restart the server, but the Exchange services will be restarted. Click here to download the update:
The update should be installed as soon as possible.