SharePoint Server 2016

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To enhance security September 2025 CU for SharePoint restricts the Windows WSS_WPG windows security group and the IIS_IUSRS windows security group from writing into the SharePoint _LAYOUTS directory (c:\program files\common files\microsoft shared\Web Server Extensions\16\TEMPLATE\LAYOUTS). As the SharePoint Configuration wizard adds the local system account of Windows (NT Authority\system) to the WSS_WPG windows security group, future […]

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SharePoint Server 2025 CU for SharePoint Server 2016, 2019 and Subscription Edition includes security hardening for SharePoint Server 2013 workflows which enforces the most recent SharePoint Workflow Manager updates to be installed on SPWFM. As a side effect this also prevents classic workflow manager workflows from running as this version does not comply with this […]

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After installing SharePoint Workflow Manager August 2025 CU on a machine which does not have a recent patch level of SharePoint Server Subscription Edition installed error messages similar to the following can be found in the logs: Could not load file or assembly ‘System.Memory, Version=4.0.1.1, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51’ or one of its dependencies. Reference: Trending Issue: […]

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Important: If September 2025 CU for SharePoint has been installed before, remove the NT Authority\system account from WSS_WPG and IIS_IUSRS local security groups of the SharePoint machines – otherwise installing the SharePoint fixes will fail. For more details check this article: Trending Issue: SharePoint fixes fail to install after installation of September 2025 CU Below […]

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Important: If September 2025 CU for SharePoint has been installed before, remove the NT Authority\system account from WSS_WPG and IIS_IUSRS local security groups of the SharePoint machines – otherwise installing the SharePoint fixes will fail. For more details check this article: Trending Issue: SharePoint fixes fail to install after installation of September 2025 CU The […]

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Since multiple Trending Issues have now been documented for the September 2025 CU, and it’s becoming increasingly difficult for individuals to keep track, I’ve decided to create a single summary page. Issue Status SharePoint 2013 Workflows fail in combination with Classic Microsoft Workflow Manager after September 2025 CU Warning: Upgrade to SPWFM required before July […]

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Several customers have reported issues when deploying custom solutions after installing the September 2025 CU for SharePoint Server 2016, 2019, and Subscription Edition. The following error is returned when deploying the solution: Cause The cause of this issue is a combination of new permissions assigned to the WSS_WPG and IIS_IUSRS Windows security groups — intended […]

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Trending Issue: SharePoint fixes fail to install after installation of September 2025 CU

Information: The issue described in this article currently affects only customers which executed the SharePoint Configuration Wizard after installing the language independent fix from September 2025 CU and the installation of the language dependent fix. Starting with October 2025 CU for SharePoint Server (all versions) most customers might be affected by this problem – so […]

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Trending Issue: Classic Workflow Manager Workflows fail after September 2025 CU for SharePoint

SharePoint Server 2025 CU for SharePoint Server 2016, 2019 and Subscription Edition includes security hardening for SharePoint Server 2013 workflows which enforces the most recent SharePoint Workflow Manager updates to be installed on SPWFM. As a side effect this also prevents classic workflow manager workflows from running as this version does not comply with this […]

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Trending Issue: "Copy SideBySide files for In Place Upgrade failed" when running SharePoint Configuration Wizard

I have received several reports from users that after installing September 2025 CU for SharePoint Server 2016, 2019 or Subscription Edition the SharePoint configuration wizard failed with the following error message: System.InvalidOperationException was thrown. Additional exception information: An internal error occurred. The program cannot continue to run. The program stopped because of the following: Copy […]

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New Security Features released with September 2025 CU for all supported SharePoint Versions

To enhance security of SharePoint Server, three new security features are being introduced in September 2025 CU. These enhancements apply to all supported SharePoint versions — 2016, 2019, and Subscription Edition — and I’d like to highlight them in this article: Machine Key Rotation Timer job AMSI enabled for all web applications Test-DefenderAndAmsiWorkProperly Cmdlet to […]