Cumulative Update 2 for Exchange Server 2013 resolves issues that were found in Exchange Server 2013 CU1 since the software was released.
Download Exchange Server 2013 RTM Cumulative Update 2 (CU2) at the Microsoft Download Center
For details read MS Exhange team blog: http://blogs.technet.com/b/exchange/archive/2013/07/09/released-exchange-server-2013-rtm-cumulative-update-2.aspx