Assume that you apply Microsoft Exchange Server 2013 Cumulative Update 5 in your environment that contains Exchange servers in multiple Active Directory sites. You open the Exchange Management Shell (EMS) for the first time, and then run a command in it. In this situation, EMS takes a long time to return the result. When this issue occurs, Exchange Admin Center (EAC) may not work, either.
This issue does not occur in an environment that has Exchange Server 2013 Service Pack 1 (SP1) or an earlier update installed.
This issue does not affect the commands that are run later.
To resolve this issue, install the following cumulative update:
2961810 Cumulative Update 6 for Exchange Server 2013
This issue occurs because Cumulative Update 5 queries all the global catalog servers in the forest.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.