Microsoft has confirmed a critical issue affecting Windows Server 2025 systems after installing October 2025 security updates. The problem disrupts Active Directory directory synchronization, particularly impacting large organizations with over 10,000 members in their AD security groups.
The issue causes incomplete results when synchronizing large AD security groups, potentially leaving user accounts and permissions unsynchronized. Microsoft has acknowledged the problem and is investigating a permanent solution. In the meantime, administrators can apply a temporary workaround by modifying the Windows registry.
However, this approach requires experienced administrators and comes with risks of serious problems requiring operating system reinstallation. Organizations may need to wait for an official patch from Microsoft or carefully evaluate their synchronisation requirements before deploying the October 2025 updates.
Source: https://gbhackers.com/microsofts-october-2025-patches-disrupt-active-directory-sync