A recent Microsoft patch is causing authentication problems for domain-joined Windows PCs, according to The Register. The culprit is a Machine Identity Isolation policy that can reject valid credentials when the domain controller is not running at the Windows Server 2025 functional level.
Administrators are seeing trust-related failures even though the credentials being presented are valid. The issue appears to stem from the patch enforcing stricter machine identity checks than before, rather than from actual account or password problems.
The Register notes that the policy expects domain controllers to be at the Server 2025 functional level. Until that requirement is met, affected machines may continue to have their credentials rejected, making the domain controller upgrade the likely path to resolution.