An improper honoring of XML External Entities was found in Microsoft Active Directory Federation Services (ADFS). By exploiting this vulnerability malicious users can obtain sensitive information. This vulnerability can be exploited remotely via a specially designed request.
Windows Server 2008
Windows Server 2008 R2
Windows Server 2012
Windows Server 2012 R2
Install necessary updates from the KB section, that are listed in your Windows Update (Windows Update usually can be accessed from the Control Panel)