Windows 11 405 Published by

Microsoft has released Windows 11 Insider Preview Build 25951 to Windows Insiders in the Canary Channel.





Announcing Windows 11 Insider Preview Build 25951 (Canary Channel)

Hello Windows Insiders, today we are releasing Windows 11 Insider Preview Build 25951 to the Canary Channel. 

What’s new in Build 25951

SMB NTLM Blocking

Starting with this build (Build 25951), the SMB client now supports blocking NTLM for remote outbound connections. This changes legacy behavior, where Windows  SPNEGO would negotiate Kerberos, NTLM, and other mechanisms with the destination server to decide on a supported security package. NTLM in this case refers to all versions of the LAN Manager security package:  LM, NTLM, and NTLMv2.

With this new option, an administrator can intentionally block Windows from offering NTLM via SMB. An attacker who tricks a user or application into sending NTLM challenge responses to a malicious server will no longer receive any NTLM data and cannot brute force, crack, or pass a password, as they will never be sent over the network. This adds a new level of protection for enterprises without a requirement to  entirely disable NTLM usage in the OS. You can configure this option with Group Policy and PowerShell. You can also block the use of NTLM in SMB connections on demand with NET USE and PowerShell.

For more information on configuring and troubleshooting NTLM blocking, review  https://aka.ms/SmbNtlmBlock.

SMB Dialect Management

Starting with this build (Build 25951), the SMB server now supports controlling which SMB 2 and 3 dialects it will negotiate. This changes legacy behavior, where Windows SMB always negotiated the highest matched server dialect from SMB 2.0.2 to 3.1.1 clients. Beginning in Windows 10, support was added for  controlling SMB client dialects, but not server dialects.

With this new option, an administrator can remove older SMB protocols from usage in the organization, blocking older, less secure, and less capable Windows devices and third parties from connecting.

You can configure this option with Group Policy and PowerShell. Both SMB client and server now include complete management support (previously the client support was only  manual registry editing).

For more information on understanding and configuring SMB dialects, review  https://aka.ms/SmbDialectManage.



Announcing Windows 11 Insider Preview Build 25951 (Canary Channel)