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 29 August 2025 may disrupt the operating system’s authentication mechanisms, specifically Kerberos and NTLM. The article explains that Microsoft uses Security Identifiers (SIDs) to track accounts and that a new enforcement mechanism requires strict SID verification, which can cause authentication handshakes to fail when duplicate SIDs are detected across devices.

This can manifest as failed logins, erroneous credential prompts during Remote Desktop sessions, or messages about machine ID mismatches, with event messages such as SEC_E_NO_CREDENTIALS. Microsoft advises enterprise IT administrators to rebuild systems exhibiting duplicate SIDs using officially supported Windows cloning or deployment methods to resolve the issue. Administrators may also request access to a special policy configuration that temporarily bypasses the problem by contacting Microsoft Support directly.