how to fix sharepoint 2019 security update that impact work flow failed to start?

Hi @Tong Chang-張耿通

Could you please confirm which workflow platform you are using (SharePoint 2010-style workflows or SharePoint Workflow Manager/2013 workflows)?

From my findings, there are multiple reports of issues affecting SharePoint 2010-style workflows after installing the June 2026 SharePoint security updates. As a first step, please review the ULS logs and check whether you see similar entries to those described in this article: Trending Issue: SharePoint 2010 Workflows fail after June 2026 CU

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If your environment is affected by this issue, Microsoft has indicated that a fix for the workflow issue is planned to be released with July 2026 CU for all supported SharePoint version.

A workaround is currently available; however, it should only be applied after careful consideration, as it disables a significant number of security protections for SharePoint 2010-style workflows that have been introduced over the last several years.

Please run the following commands in the SharePoint Management Shell as a farm administrator:

$farm = Get-SPFarm
$farm.EnablePreParseSecurityCheckForWorkflow = $false
$farm.Update()
iisreset

After IIS has restarted, please test the affected workflow again.

On the other hand, if you are using SharePoint Workflow Manager (2013 platform workflows), please note that Microsoft requires the SharePoint Workflow Manager update (KB5002799) to be installed on the Workflow Manager farm before installing the June 2026 SharePoint cumulative update as mentioned in Description of the Security Update for SharePoint Server 2019 (KB5002874).

Please let me know any relevant ULS log entries generated when attempting to start the workflow. This information will help determine the appropriate resolution path.

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I tested for the released fixed with July 2026 CU, but it still gave the failed on start, I implemented the turn arount the workflow now keeping "In progress". My workflow is 2010 workflow. May be there will be another fix for this in the coming moths?