Microsoft Confirms October 2026 Patch Tuesday Breaks Wi-Fi and VPN

Microsoft has confirmed that the October 2026 Patch Tuesday updates can cause authentication failures on some Wi-Fi, Ethernet, and VPN connections.

The problem stems from Microsoft’s decision to enforce restrictions on legacy NTLMv1 authentication by default. According to Microsoft’s documentation, the change affects Windows 11 versions 24H2, 25H2, and 26H2, along with Windows Server 2025.

Networks that rely on MS-CHAPv2 authentication, including some WPA-Enterprise Wi-Fi configurations and VPN connections, may fail to authenticate after users install the updates.

Why the October updates cause authentication failures

The October 13 security updates, including KB5127648 for Windows 11 and KB5126646 for Windows Server 2025, automatically enforce NTLMv1 restrictions on systems where Credential Guard is disabled.

Previously, Windows used Audit mode by default, which allowed legacy authentication to continue while recording warnings. The new enforcement behavior blocks authentication attempts that rely on NTLMv1-derived credentials.

Microsoft introduced the BlockNtlmv1SSO registry setting in August 2025 to give administrators control over these restrictions. In September 2025, the company also added auditing capabilities to help organizations identify authentication systems that still depend on NTLMv1.

Microsoft provides a temporary workaround

Administrators experiencing connection failures can temporarily restore Audit mode by changing the BlockNtlmv1SSO registry value to 0.

The setting is located at:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0

Setting the value to 0 allows affected systems to authenticate using legacy NTLMv1-derived Single Sign-On credentials. Administrators may need to restart the affected devices for the change to take effect.

However, Microsoft warns that restoring Audit mode weakens security protections. Organizations should only use this workaround temporarily and prioritize migrating affected Wi-Fi, VPN, and network authentication configurations away from legacy NTLMv1-based methods.

The authentication issue is not the only problem associated with Microsoft’s October updates. Users have also reported Xbox Live sign-in error 0x87DD0005 after installing KB5127648 and KB5127694.

Meanwhile, Microsoft’s October 2026 Patch Tuesday addresses 1,411 vulnerabilities, making the latest security updates particularly significant despite the reported problems.

Via Neowin