Microsoft has confirmed a critical issue affecting Windows Server 2025 systems following the installation of October 2025 security updates.
The problem disrupts Active Directory directory synchronization, specifically impacting organizations managing large security groups with more than 10,000 members.
Directory Sync Failures Impact Large Organizations
The synchronization failure affects applications that rely on the Active Directory directory synchronization control, commonly known as DirSync, for on-premises Active Directory Domain Services.
Organizations using Microsoft Entra Connect Sync to bridge on-premises directories with cloud services are particularly vulnerable to this issue.
When attempting to synchronize large AD security groups exceeding 10,000 members, the process returns incomplete results, potentially leaving critical user accounts and permissions unsynchronized.
Microsoft officially acknowledged the problem on October 14, 2025, stating that the issue first appeared after installing the September 2025 Windows security update labeled KB5065426.
Subsequent updates released in October have continued to exhibit the same behavior, leaving administrators with limited options for maintaining normal operations.
The timing suggests many organizations may have already deployed the problematic updates to production environments.
While Microsoft investigates a permanent solution, affected organizations can implement a temporary workaround by modifying the Windows registry.
The fix involves disabling a specific feature change that appears responsible for the synchronization failures. Administrators need to create a new DWORD value named 2362988687 with a value of 0 under the FeatureManagement Overrides section located at HKEY_LOCAL_MACHINE.
Microsoft has issued a strong warning about the registry modification approach, emphasizing that incorrect registry changes can cause serious problems requiring operating system reinstallation.
The company recommends that only experienced administrators familiar with Windows registry operations attempt this workaround.
Organizations uncomfortable with registry modifications may need to wait for an official patch from Microsoft.
Microsoft has not provided a specific timeline for releasing a permanent fix to address the directory synchronization issue.
The company stated it is investigating the problem and will deliver a resolution through a future Windows update.
This uncertainty leaves enterprise administrators in a difficult position, forced to choose between applying critical security updates and maintaining reliable directory synchronization.
The issue exclusively affects Windows Server 2025 installations, with no reports of similar problems on client versions of Windows or earlier server editions.
Organizations still running Windows Server 2022 or older versions remain unaffected by this particular synchronization failure.
System administrators managing large Active Directory environments should carefully evaluate their synchronisation requirements before deploying October 2025 updates to production domain controllers.
Those who have already experienced synchronization failures can immediately apply the registry workaround while monitoring Microsoft’s official channels for news about a permanent resolution.
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