The Cumulative Update 3 for Exchange 2013 has been released. As with all Exchange 2013 updates, this is the complete installation package with which new servers can also be installed.
The update can be downloaded here:
With CU3, Internet Explorer 11 is now also supported as a premium client for OWA. A complete description of all hotfixes can be found here:
http://support.microsoft.com/kb/2892464
Incidentally, Service Pack 1 for Exchange 2013 is due to be released in the first quarter of 2014.