This security update resolves vulnerabilities in Windows that could allow remote code execution in a host context if a specially crafted application is run by an authenticated and privileged user on a guest virtual machine that is hosted by Hyper-V. An attacker must have valid logon credentials for a guest virtual machine to exploit this vulnerability. To learn more about the vulnerability, see Microsoft Security Bulletin MS15-068.
All future security and nonsecurity updates for Windows 8.1 and Windows Server 2012 R2 require update 2919355 to be installed. We recommend that you install update 2919355 on your Windows 8.1-based or Windows Server 2012 R2-based computer so that you receive future updates.
If you install a language pack after you install this update, you must reinstall this update. Therefore, we recommend that you install any language packs that you need before you install this update. For more information, see Add language packs to Windows.
How to obtain and install the update
Method 1: Windows Update
This update is available through Windows Update. When you turn on automatic updating, this update will be downloaded and installed automatically. For more information about how to turn on automatic updating, see Get security updates automatically.
Method 2: Microsoft Download Center
You can obtain the stand-alone update package through the Microsoft Download Center. Follow the installation instructions on the download page to install the update.
The English (United States) version of this software update installs files that have the attributes that are listed in the following tables. The dates and times for these files are listed in Coordinated Universal Time (UTC). The dates and times for these files on your local computer are displayed in your local time and with your current daylight saving time (DST) bias. Additionally, the dates and times may change when you perform certain operations on the files.
Windows 8.1 and Windows Server 2012 R2 file information
The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:
6.3.920 0.16 xxx
Windows 8.1 and Windows Server 2012 R2
GDR service branches contain only those fixes that are widely released to address widespread, critical issues. LDR service branches contain hotfixes in addition to widely released fixes.
Note The MANIFEST files (.manifest) and MUM files (.mum) that are installed are not listed.
For all supported x64-based versions of Windows 8.1 and Windows Server 2012 R2
How to obtain help and support for this security update