Networking problems after the October 2026 Windows update? NTLM might be to blame
Legacy protocol is going to be axed, and enforcement by default will highlight how migration is going
Windows users who continue to rely on the outdated NTLMv1 security protocol may encounter network connectivity issues after the October 2026 Windows security update. This update blocks NTLMv1-derived credentials, which were previously permitted for Single Sign-On, leading to blocked requests and potential impacts on Wi-Fi, Ethernet, and VPN authentication.
The BlockNtlmSSO registry value is responsible for this change, and if not set, Windows defaults to Enforce mode (1) instead of Audit mode (0). Microsoft advises administrators to set BlockNtlmSSO to 0 temporarily to allow NTLMv1-derived Single Sign-On credentials, but warns that using Audit mode reduces protection and should only be considered a temporary security exception.
Microsoft has been phasing out NTLM since 2024, stating its long-term goal is to eliminate the need for NTLM entirely, and it has already removed the technology from Windows 11 24H2 and Windows Server 2025. The update occurring in 2026 is the next step in enforcing this deprecation.
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