Be aware that all Updates for SharePoint 2013 require March 2013 PU for SharePoint 2013 to be installed first.
SharePoint Foundation 2013
2849961 The full server package for SharePoint Foundation 2013
SharePoint Server 2013
2850024 The full server package for SharePoint Server 2013 and contains also the SharePoint Foundation 2013 fixes so you need only this package.
Please read carefully the KB article first before you download and install the CU!
And the new Blog post from our Sustain Engineering team: http://blogs.technet.com/b/office_sustained_engineering/archive/2013/12/20/change-sharepoint-2013-rollup-update-for-the-december-2013-cumulative-update-packaging.aspx
Office Web Apps Server 2013
2850013 Microsoft Office Web Apps Server 2013 hotfix package
SharePoint Designer 2013
2837671 SharePoint Designer 2013 hotfix package
Project Server 2013
xxxxxx The full server package for Project Server 2013 and contains also the SharePoint Server and Foundation 2013 fixes so you need only this package.
Not yet available.
Important for all Server Applications listed above:
After applying the preceding updates, run the SharePoint Products and Technologies Configuration Wizard or “psconfig –cmd upgrade –inplace b2b -wait” in command line. This needs to be done on all servers in the farm with SharePoint installed. You can run psconfig in parallel on all SharePoint machines.
You might have you own strategy to run psconfig because it depends on the farm structure and what makes sense to reduce the downtime.