July 10, 2018—KB4338824 (Security-only update)

Improvements and fixes

This security update includes quality improvements. No new operating system features are being introduced in this update. Key changes include:

• Provides protections from an additional subclass of speculative execution side-channel vulnerability known as Speculative Store Bypass (CVE-2018-3639). These protections aren’t enabled by default. For Windows client (IT pro) guidance, follow the instructions in KB4073119. For Windows Server guidance, follow the instructions in KB4072698. Use this guidance document to enable mitigations for Speculative Store Bypass (CVE-2018-3639) in addition to the mitigations that have already been released for Spectre Variant 2 (CVE-2017-5715) and Meltdown (CVE-2017-5754).
• Provides support to control usage of Indirect Branch Prediction Barrier (IBPB) on some AMD processors (CPUs) for mitigating CVE-2017-5715, Spectre Variant 2 when switching from user context to kernel context. (See AMD Architecture Guidelines for Indirect Branch Control and AMD Security Updates for more details). For Windows client (IT pro) guidance, follow the instructions in KB4073119. Use this guidance document to enable IBPB on some AMD processors (CPUs) for mitigating Spectre Variant 2 when switching from user context to kernel context.
• Provides protections for an additional vulnerability involving side-channel speculative execution known as Lazy Floating Point (FP) State Restore (CVE-2018-3665) for 64-Bit (x64) versions of Windows.
• Security updates to Windows apps, Windows graphics, Windows Shell, Windows datacenter networking, Windows virtualization, and Windows kernel.
  For more information about the resolved security vulnerabilities, see the Security Update Guide.

Known issues in this update

How to get this update

This update is now available for installation through WSUS. To get the stand-alone package for this update, go to the Microsoft Update Catalog website.File informationFor a list of the files that are provided in this update, download the file information for update 4338824.