KB5002856:security update resolves Microsoft SharePoint Server spoofing vulnerability.

Description of the security update for SharePoint Server 2019 Language Pack: April 14, 2026 (KB5002856)

Summary
Important:

If you're running 2013-type workflows, you mustinstall the August 2025 update for SharePoint Workflow Manager​​​​​​​to your farm before you install this cumulative update.

If you're currently running the Classic version of Workflow Manager, you must enable the debug flag to continue using it.
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$farm = Get-SPFarm
$farm.ServerDebugFlags.Add(53601)
$farm.update()
iisreset

This security update resolves Microsoft SharePoint Server spoofing vulnerability. To learn more about the vulnerability, see Microsoft Common Vulnerabilities and Exposures CVE-2026-​​​​20945.

Notes:

• This is build 16.0.10417.20114 of the security update package.
• To apply this security update, you must have the release version of Microsoft SharePoint Server 2019 installed on the computer.