Networking Problems After the October 2026 Windows Update? NTLM Might Be to Blame
The Register, Friday, October 16th, 2026
October's Windows update now blocks NTLMv1-derived credentials by default, which can break Wi-Fi, Ethernet and VPN logons.
Before the October 2026 Windows security update, NTLMv1-derived credentials for single sign-on were allowed with warning events.
Now, if the BlockNtlmSSO registry value is unset and Credential Guard is not enabled, Windows uses Enforce mode and blocks them, potentially breaking Wi-Fi, Ethernet and VPN authentication.
Remnants often surface with MS-CHAPv2-based connections such as PEAP-MSCHAPv2 in domain-joined environments.
Admins can set Audit mode as a temporary exception, but Microsoft says the change is by design as it finalizes NTLMv1 disablement, so migration should not wait.