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This security update resolves a Microsoft Office Online Server spoofing vulnerability and Microsoft Excel remote code execution vulnerability. To learn more, see Microsoft Common Vulnerabilities and Exposures CVE-2021-34451 and Microsoft Common Vulnerabilities and Exposures CVE-2021-34501.

Note: To apply this security update, you must have the release version of Microsoft Office Online Server installed on the computer.

Improvements and fixes

Note: Support for Windows Server 2019 has been added for Office Online Server.

Using TLS 1.1 and TLS 1.2 together with Office Online Server requires strong cryptography in .NET Framework 4.5 and later versions. This update enables the strong cryptography in .NET Framework 4.5 or later by adding the following registry keys. After you install this update, you don't have to manually enable strong cryptography, as you would otherwise have to do by following the steps in the first section of Enable TLS 1.1 and TLS 1.2 support in Office Online Server.

Windows Registry Editor Version 5.00



How to get and install the update

Method 1: Microsoft Update

This update is available from Microsoft Update. When you turn on automatic updating, this update will be downloaded and installed automatically. For more information about how to get security updates automatically, see Windows Update: FAQ.

Method 2: Microsoft Update Catalog

To get the standalone package for this update, go to the Microsoft Update Catalog website.

Method 3: Microsoft Download Center

You can get the standalone update package through the Microsoft Download Center. Follow the installation instructions on the download page to install the update.

More information

Security update deployment information

For deployment information about this update, see Security update deployment information: July 13, 2021 (KB5004480).

Security update replacement information

This security update replaces previously released security update 5001943.

File hash information

File name

SHA256 hash



File information

Download the list of files that are included in security update 5001973.

Information about protection and security

Protect yourself online: Windows Security support

Learn how we guard against cyber threats: Microsoft Security

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