October 8, 2019—KB4520003 (Security-only update)

IMPORTANT Verify that you have installed the required updates listed in the How to get this update section before installing this update.

IMPORTANT Customers who have purchased the Extended Security Update (ESU) for on-premises versions of some operating systems must follow specific procedures to continue receiving security updates after extended support ends on January 14, 2020. For more information, see KB4522133.

Improvements and fixes

This security update includes quality improvements. Key changes include:

Addresses an issue in security bulletin CVE-2019-1318 that may cause client or server computers that don’t support Extended Master Secret (EMS) RFC 7627 to have increased connection latency and CPU utilization. This issue occurs while performing full Transport Layer Security (TLS) handshakes from devices that don’t support EMS, especially on servers. EMS support has been available for all the supported versions of Windows since calendar year 2015 and is being incrementally enforced by the installation of the October 8, 2019 and later monthly updates.
Security updates to Windows Authentication, Microsoft JET Database Engine, Windows Kernel, Internet Information Services, and Windows Server.

For more information about the resolved security vulnerabilities, please refer to the Security Update Guide.

Known issues in this update

Symptom

Workaround

Updates for Windows released October 8, 2019 or later provide protections, tracked by CVE-2019-1318, against an attack that could allow unauthorized access to information or data within TLS connections. This type of attack is known as a man-in-the-middle exploit. Windows might fail to connect to TLS clients and servers that do not support Extended Master Secret for resumption (RFC 7627). Lack of RFC support might cause one or more of the following errors or logged events:

"The request was aborted: Could not create SSL/TLS secure Channel"

SCHANNEL event 36887 is logged in the System event log with the description, "A fatal alert was received from the remote endpoint. The TLS protocol defined fatal alert code is 20."

For information, see KB4528489.

How to get this update

Before installing this update

Prerequisite:

You must install the updates listed below and restart your device before installing the latest Rollup. Installing these updates improves the reliability of the update process and mitigates potential issues while installing the Rollup and applying Microsoft security fixes.

The March 12, 2019 servicing stack update (SSU) (KB4490628). To get the standalone package for this SSU, search for it in the Microsoft Update Catalog.
The latest SHA-2 update (KB4474419) released September 10, 2019. If you are using Windows Update, the latest SHA-2 update will be offered to you automatically. For more information on SHA-2 updates, see 2019 SHA-2 Code Signing Support requirement for Windows and WSUS.
The latest SSU (KB4516655). If you are using Windows Update, the latest SSU will be offered to you automatically. To get the standalone package for the latest SSU, search for it in the Microsoft Update Catalog.

Install this update

Release Channel	Available	Next Step
Windows Update and Microsoft Update	No	See the other options below.
Microsoft Update Catalog	Yes	To get the standalone package for this update, go to the Microsoft Update Catalog website.
Windows Server Update Services (WSUS)	Yes	This update will automatically synchronize with WSUS if you configure Products and Classifications as follows: Product: Windows 7 Service Pack 1, Windows Server 2008 R2 Service Pack 1 Classification: Security Updates

File information

For a list of the files that are provided in this update, download the file information for update 4520003.

October 8, 2019—KB4520003 (Security-only update)

Improvements and fixes

Known issues in this update

How to get this update

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