Microsoft has released a Microsoft security advisory about this issue for IT professionals. The security advisory contains additional security-related information. To learn more about the vulnerability, see Microsoft security advisory (4010323): SHA-1 deprecation for SSL/TLS certificates.
All future security and non-security 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.
This fix is included in the following updates:
May 9, 2017—KB4019215 (OS Build .001)
May 9, 2017—KB4019264 (OS Build .002)
May 9, 2017—KB4019474 (OS Build .001)
May 9, 2017—KB4019472 (OS Build .002)
May 9, 2017—KB4016871 (OS Build .002)
May 9, 2017—KB4019473 (OS Build .001)
May 9, 2017—KB4019214 (OS Build .002)
May 9, 2017—KB4019263 (OS Build .002)
May 9, 2017—KB4019213 (OS Build .002)
May 9, 2017—KB4019216 (OS Build .003)
Help for installing updates: Support for Microsoft Update
Security solutions for IT professionals: TechNet Security Troubleshooting and Support
Help for protecting your Windows-based computer from viruses and malware: Virus Solution and Security Center
Local support according to your country: International Support