Microsoft's October Windows update blocks NTLMv1 single sign-on through a setting called BlockNtlmSSO, according to the source report.
NTLMv1 is a legacy authentication protocol. Administrators who still depend on it may see sign-in failures after the update.
Source: theregister.com, reported 10-16. https://www.theregister.com/security/2026/10/16/networking-problems-after-the-october-2026-windows-update-ntlm-might-be-to-blame/5303503