Microsoft Acknowledges Kerberos and NTLM Login Issues in Windows 11 and Server 2025

Microsoft has confirmed a significant issue with Kerberos and NTLM authentication on Windows 11 (versions 24H2 and 25H2) and Windows Server 2025 systems. The problem is attributed to devices sharing duplicate Security IDs (SIDs), which has resulted in widespread login failures.

The issue emerged after users installed recent cumulative updates, including:

These updates introduced new security measures aimed at enforcing the uniqueness of SIDs, leading to authentication breakdowns on systems that were improperly cloned or duplicated.

Affected users are experiencing a range of issues, including:

  • Continual credential prompts and failed logins
  • Inaccessibility to shared network folders
  • Errors with Remote Desktop Protocol (RDP) connections
  • Failures in Failover Clustering operations accompanied by “access denied” messages
  • Anomalies in the Event Viewer, with errors such as SEC_E_NO_CREDENTIALS and "partial mismatch in the machine ID."

The root cause has been identified as duplicated SIDs, which often arise when administrators clone Windows installations without the proper use of Sysprep. This tool ensures that each device has a unique identifier necessary for Microsoft’s security protocol. The new updates have tightened enforcement, blocking authentication entirely when duplicates are detected, a change that was deliberate but has disrupted many enterprise environments relying on duplication methods.

To address this issue, Microsoft suggests rebuilding affected systems using supported methods that generate unique SIDs. For IT administrators seeking a temporary fix, the company is offering a special Group Policy to disable SID enforcement, available only by contacting Microsoft Support for Business.

This situation highlights the ongoing challenges faced by enterprise IT departments as they navigate the updates to Windows 11 and Server 2025.

For additional information, users may refer to Microsoft’s complete support guide.


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