Windows updates since August 29, 2025, have disrupted authentication for systems with duplicate Security Identifiers (SIDs), affecting Windows 11 and Windows Server 2025 users.
Authentication Issues and Errors
The updates implemented added security measures that check for duplicate SIDs, which prevent proper authentication. This block can cause issues like failed Remote Desktop connections and 'access denied' errors.
- Kerberos and NTLM authentication failures are common.
- Errors such as 'Login attempt failed' may appear.
- Event Viewer may log SEC_E_NO_CREDENTIALS warnings.
Duplication and Solutions
Duplicate SIDs often arise from improperly cloned Windows installations. Microsoft advises using the Sysprep tool to ensure unique SIDs in OS duplications. Systems affected must be rebuilt using supported Windows installation methods.
An interim solution involves configuring a special Group Policy via Microsoft Support, specifically designed for business environments.
