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vulnerabilities
Networking problems after the October 2026 Windows update? NTLM might be to blame
Microsoft's October 2026 Windows security update changes the default behavior of NTLMv1 authentication from audit mode to enforce mode, blocking requests that use NTLMv1-derived credentials for Single Sign-On. This change may disrupt networking, including Wi-Fi, Ethernet, and virtual private network (VPN) authentication for organizations that have not completed migration away from the deprecated technology. Administrators can temporarily revert to audit mode by setting the BlockNtlmSSO registry value to 0, though Microsoft notes this reduces security and views the change as part of its broader effort to eliminate NTLM entirely from Windows.
Why it matters: Windows administrators and enterprises still using NTLMv1 or MS-CHAPv2-based authentication should urgently test the October 2026 update in their environments to identify connectivity failures and plan migration away from the legacy protocol before workarounds are removed in future Windows releases.
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