Some scenarios of SharePoint 2010 workflow are affected after applying the July security update for SharePoint Server (KB5004862)

Symptoms

After you install the following July security updates for SharePoint Server, existing Microsoft SharePoint 2010 workflows stop functioning. When this issue occurs, "c42q8," "c42ra," or "c42rh" event tags are logged in the SharePoint Unified Logging System (ULS) log.

• Description of the security update for SharePoint Server 2019: July 13, 2021 (KB5001975)

• Description of the security update for SharePoint Enterprise Server 2016: July 13, 2021 (KB5001976)

• Description of the security update for SharePoint Foundation 2013: July 13, 2021 (KB5001992)

Cause

This issue occurs because an additional validation was added in the July security update for SharePoint Server. The validation causes the existing SharePoint 2010 workflows to stop functioning.

Workaround

To work around this issue, locate the "c42q8," "c42ra," or "c42rh" event tags in the SharePoint ULS log. In these event entries, you can find details about why the workflow is blocked, per these guidelines:

• If the blocked parts are "out of the box" workflows or workflow activities, contact Microsoft Support.
  
  Additionally, you can contact the farm administrator to temporarily disable the additional validation by using PowerShell: 
  
  In PowerShell, run the following cmdlets:
  
  Add-PSSnapin Microsoft.SharePoint.PowerShell
  $farm=Get-SPFarm
  $farm.EnablePreParseSecurityCheckForWorkflow = $false
  $farm.update()

• If the blocked parts are written by using custom code, and you deploy them yourself in SharePoint Server, you should do a security review on the type that you’re trying to use. If that type is determined to be safe, you can add it to the web.config’s list of authorized types. Otherwise, you should create an alternative implementation that does not violate the security validations.