Critical Windows Update Bug Breaks Kerberos and NTLM Authentication

According to a support bulletin released by Microsoft, updates to Windows 11 24H2/25H2 and Windows Server 2025 issued after August 29, 2025, may disrupt the operating system’s authentication mechanisms, specifically affecting Kerberos and NTLM authentication protocols.

In Windows 10 and Windows 11, Microsoft employs Security Identifiers (SIDs) to track and manage user accounts, groups, and computer accounts. The system internally relies on SIDs for access control, permission management, and security auditing—rather than depending on administrator account names.

In its latest update, Microsoft has introduced a new security enforcement mechanism that mandates strict SID verification. When duplicate SIDs are detected across devices, authentication may fail, as this design change prevents successful authentication handshakes between affected systems.

These issues can manifest as various anomalies during user operations, such as:

• Failed login attempts despite the use of correct authentication credentials
• Errors or invalid credential prompts during Remote Desktop sessions
• Authentication failures or expired credentials when accessing network resources
• Additional error messages indicating machine ID mismatches or incorrect usernames or passwords

On affected devices, such errors may appear in the Event Viewer or Local Security Authority Server with codes similar to SEC_E_NO_CREDENTIALS, accompanied by messages like “There is a partial mismatch in the machine ID. This indicates that the ticket has either been manipulated or it belongs to a different boot session.”

Microsoft advises enterprise IT administrators to rebuild systems exhibiting duplicate SIDs using officially supported Windows cloning or deployment methods to resolve authentication issues. Administrators may also request access to a special policy configuration that temporarily bypasses the problem—though this workaround is only available by contacting Microsoft Support directly.

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• Critical Microsoft Access Vulnerability Exploited for NTLM Token Theft
• Microsoft’s August Patch Tuesday: Zero-Day Kerberos Flaw Threatens Domain Admins
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