The product group released the April 2013 Cumulative Update for the SharePoint 2013 product family.
Be aware that all Update for SharePoint 2013 require March 2013 PU for SharePoint 2013 to be installed first.
The KB articles for April CU will be availabe at the following locations in a couple of days:
KB 2751999 – SharePoint Foundation 2013
KB 2726992 – SharePoint Server 2013
KB 2775426 – SharePoint Server 2013 with Project Server
KB 2799821 – Office Web Apps Server 2013
The Full Server Packages for April 2013 CU are available through the following links:
Download SharePoint Foundation 2013 April 2013 CU
Download SharePoint Server 2013 April 2013 CU
Download Project Server 2013 April 2013 CU
Download Office Web Apps Server 2013 April 2013 CU
After installing the fixes you need to run the SharePoint 2013 Products Configuration Wizard on each machine in the farm as mentioned here for 2013 and here for 2010.
An up to date list provided by Microsoft could be found here.