​Microsoft has released the Windows 10 1909 KB5000850 cumulative update preview and a new KB5001205 Servicing Stack Update that resolves a Secure Boot vulnerability.

The KB5001205 Servicing Stack Update (SSU) will automatically be installed by Windows Update to improve the update experience. This SSU should not be skipped as it fixes an issue installing a previously released Secure Boot security update.

Also released yesterday is Windows 10 1909 KB5000850 (build 18363.1474), the March 2021 non-security preview “C” update that allows users and businesses to test upcoming fixes before they are released to everyone during the April 2021 Patch

As this is an optional update, Windows 10 will not install it automatically. Instead, users will need to open Windows Update, check for updates, and select to install the preview update when it is offered.

SSU update fixes security update issue

When Microsoft finds bugs related to Windows Update, they release servicing stack updates to resolve the issues and provide a more reliable updating experience.

With the release of the KB5001205 SSU, Microsoft is fixing an issue that causes the CVE-2020-0689 Secure Boot security update not to be installed. CVE-2020-0689 is a vulnerability that could allow attackers to bypass Secure Boot and install untrusted software.

“This update also addresses an issue that might prevent the CVE-2020-0689 update from installing. The error message in the CBS.log file is TRUST_E_NOSIGNATURE. To learn more about this security vulnerability,

The SSU update fixes the issue by making sure prerequisite updates are installed in the proper order for the CVE-2020-0689 security update to install without errors.

SSU updates are mandatory and will automatically be installed by Windows 10 through Windows Update.