Microsoft has confirmed a significant login issue affecting Windows 11 (versions 24H2 and 25H2) and Windows Server 2025. This problem, which has emerged following recent cumulative updates, leads to Kerberos and NTLM authentication failures due to the presence of duplicate Security IDs (SIDs) on certain devices.
The issue became apparent after specific updates were installed, notably:
These updates introduced measures to ensure SID uniqueness, which inadvertently resulted in failed authentication for systems that were cloned without proper configuration. Affected users are reporting several problems, including:
Event Viewer may show related errors, such as SEC_E_NO_CREDENTIALS or Event ID: 6167, which signals a mismatch in machine IDs.
The root cause of the issue is traced back to duplicate SIDs typically generated when administrators clone Windows installations without utilizing the Sysprep tool, which is essential for creating unique identifiers for each deployment. Due to recent security enhancements in Windows 11, Microsoft has imposed stricter validation, completely blocking authentication when duplicate SIDs are detected.
Microsoft clarified that this change was deliberate, but it has unintentionally disrupted workflows in enterprise environments that rely on cloning techniques for virtual machines.
To resolve the issue, Microsoft recommends users check this guide and advises rebuilding affected systems using supported methods that ensure unique SIDs. As a temporary workaround, a specific Group Policy can suppress SID enforcement, but this option requires consultation with Microsoft Support for Business.
This authentication issue adds to the growing list of complications faced by businesses after deploying the latest Windows 11 and Server 2025 updates.
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