[German]A feature change causes administrators of large Active Directory environments to encounter problems when installing the September 2025 update KB5065426 for Server 2025. However, there is a workaround.
Windows Server 2025 Update KB5065426
On September 9, 2025, Microsoft released security update KB5065426 for Windows Server 2025 (see Patchday: Windows Server-Updates (September 9, 2025)). This update rolled out numerous fixes and changes, which are listed in the linked support article.
However, the Known Issues section of this support article also contains a list of known problems:
- Errors with PSDirect connections in hot patch devices
- SMBv1 protocol connectivity
- Active Directory replication
- Directory synchronization (DirSync)
Details can be found in the linked support article.
Problem with AD directory synchronization
The entry Directory synchronization (DirSync) listed above refers to a newly documented issue (via). According to the entry Directory synchronization fails for AD security groups exceeding 10,000 members in the Known Issues section of the Windows Server 2025 Release Health Dashboard dated October 14, 2025, there are issues with security update KB5065426.
Applications that use Active Directory directory synchronization (DirSync) for local Active Directory Domain Services (AD DS), such as when using Microsoft Entra Connect Sync, may result in incomplete synchronization of large AD security groups with more than 10,000 members.
This issue only occurs on Windows Server 2025 after installing the September 2025 Windows security update (KB5065426) or later updates. Affected customers can open the following registry key to disable the feature change.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Policies\Microsoft\FeatureManagement\Overrides
Set the 32-bit REG_DWORD value 2362988687 to 0. Microsoft points out that any changes to the registry are made at your own risk. Microsoft is investigating the problem and plans to release a patch in due course.
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