🔒Windows 10 Update Blocks NTLMv1, Causing Networking Issues
Your NTLMv1-based apps might break after October
TL;DR
Microsoft's October 2026 update blocks NTLMv1-derived credentials, potentially disrupting networks. Admins can temporarily allow NTLMv1 with BlockNtlmSSO set to 0, but this workaround won't last.
Microsoft's October 2026 update blocks NTLMv1-derived credentials, causing potential networking issues for those still using NTLMv1 security. This move aims to phase out NTLMv1 for better security, but it could disrupt legacy systems. Admins can temporarily allow NTLMv1 by setting BlockNtlmSSO to 0, but this workaround won't last past the next major Windows release. The update blocks requests to use NTLMv1-derived credentials, and the BlockNtlmSSO registry value determines enforcement mode. If you're still using NTLMv1, start planning your migration now.
Key Points
October 2026 update blocks NTLMv1-derived credentials, causing potential networking issues.
Admins can temporarily allow NTLMv1 by setting BlockNtlmSSO to 0, but this won't last.
NTLMv1 appeared in 1993 with Windows NT 3.1, now being phased out for better security.
Microsoft added audit logs for NTLMv1 usage in late August 2025, tracking usage.
NTLM will still be supported in in-market versions of Windows client and Windows Server.
Why It Matters
If you're still using NTLMv1 in your network, the October 2026 update will break your systems. Setting BlockNtlmSSO to 0 can temporarily fix issues, but you need a long-term plan. NTLMv1 is being phased out for better security, so migration is inevitable.
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