Microsoft’s October 2025 Patches Disrupt Active Directory Sync on Server 2025 Systems

Microsoft has confirmed a critical issue affecting Windows Server 2025 systems after installing October 2025 security updates, disrupting Active Directory directory synchronization for large security groups with more than 10,000 members. The problem affects applications that rely on DirSync for on-premises Active Directory Domain Services, with Entra Connect Sync for bridging on-premises directories to cloud services also being affected.

When large AD security groups exceed 10,000 members, synchronization returns incomplete results, potentially leaving user accounts and permissions unsynchronised, and the issue first appeared after the September 2025 Windows update KB5065426, with October updates continuing the same behaviour.

A temporary registry workaround is available, involving creating a new DWORD value named 2362988687 with a value of 0 under the FeatureManagement Overrides section at HKEY_LOCAL_MACHINE, though Microsoft warns that incorrect registry changes can cause serious problems requiring OS reinstallation. Those uncomfortable with registry modifications may wait for an official patch, and the issue appears to affect only Windows Server 2025 installations, with no reports on client Windows versions or earlier server editions.