Microsoft has now made available the latest Lync Server 2013 Cumulative Update (CU). This is not the first CU for Lync Server 2013, though Microsoft seems to be treating it as such using the same nomenclature as other product updates. The first one was released in July of 2013 and the one released today is intended as a replacement.
I'm not sure why Microsoft is having problems giving updates a number designation these days. Windows 8.1 Update 1 was labeled simply "Update," Windows 8.1 Update 2 is being named "August Update," and even the latest rev of Windows Phone 8.1 has been given the same, simple "Update" branding. It makes it harder to tell if you're implementations are running the most current revisions.
For our purposes, I'll stick with "Cumulative Update 2." CU2 is supported for those Lync Server 2013 implementations running on Windows Server 2008 R2 SP1, Windows Server 2012, and Windows Server 2012 R2.
Download the CU here: Lync Server 2013 Cumulative Update KB 2809243
To see the list of updates included in the CU, see KB article 2809243.
Microsoft intends to release Cumulative Updates (CU's) once every quarter. Each CU is truly cumulative in that it is a large hotfix that pulls together all previously released hotfixes into a single distribution. When customers need to apply the latest fixes, they only need the very latest CU.
A CU for Lync 2013 Clients was released in November 2013.