Comment on December 2015 CU for SharePoint 2013 is available for download by Stefan Goßner

Hi Feytensj,
Office client applications need to add some Vanity domain Urls for SharePoint (Online) to the trusted zone in IE to allow cross domain Office integration with SharePoint.
The Urls are added to the trusted site by the Office client using this programmatic method: https://msdn.microsoft.com/en-us/library/ms537181(VS.85).aspx
If vanity URLs change Office client needs to know about these. The fix allows dynamic updates of these Vanity URLs.
Cheers,
Stefan