Microsoft Sounds Windows 11 And Server Update Failure Alarm
REDMOND, WA – November 1, 2025 – Microsoft has issued a warning that recent Windows 11 and Windows Server updates are causing authentication failures for devices with duplicate Security Identifiers (SIDs), potentially blocking access for legitimate users. The issue stems from new security protections enforcing checks on SIDs, a unique identifier for each user and computer within a network.
The update changes are designed to bolster security by preventing unauthorized access to restricted files. Microsoft confirmed the new enforcement “enforce checks on SIDs, causing authentication to fail when devices have duplicate SIDs.” Duplicate SIDs are frequently created when Windows installations are cloned or duplicated without utilizing the Sysprep tool, a Microsoft system readiness tool.
Prior to the update, duplicated SIDs could allow an unauthorized user to access files intended for another user on the duplicated system. “This design change blocks authentication handshakes between such devices,” Microsoft stated, adding that “devices containing duplicate SIDs will need to be rebuilt using supported methods” for cloning or duplicating a Windows installation to ensure unique SIDs.
The company directs users to its troubleshooting documentation for guidance on resolving the issue: https://learn.microsoft.com/en-gb/troubleshoot/windows-server/setup-upgrade-and-drivers/windows-installations-disk-duplication.
The move underscores Microsoft’s increasing focus on security hardening within the Windows ecosystem, even if it introduces compatibility challenges for users relying on unsupported cloning practices.
(Additionally, Forbes reported today that Proton has exposed 300 million stolen credentials, with 49 including passwords: https://www.forbes.com/sites/daveywinder/2025/11/01/proton-exposes-300-million-stolen-credentials—49-include-passwords/. Forbes also recently warned of a LinkedIn DM attack: https://www.forbes.com/sites/daveywinder/2025/10/31/linkedin-dm-attack-warning—what-users-need-to-know/)
