Windows 11 Insider Preview Build 25951 Released with Enhanced Protection Measures

Windows 11 Insider Preview Build 25951

Microsoft has rolled out Windows 11 Insider Preview Build 25951 to the Canary Channel along with the relevant ISOs. The SMB client now supports blocking NTLM for remote outbound connections, which changes legacy behavior. The Windows SPNEGO would negotiate Kerberos, NTLM, and other mechanisms with the destination server to decide on a supported security package. Microsoft revealed that NTLM refers to all versions of the LAN Manager security package such as LM, NTLM, and NTLMv2.

With the help of this option, an administrator can deliberately block Windows from offering NTLM via SMB. If an attacker tricks a user or application into sending NTLM challenge responses to a malicious server, then it will no longer receive any NTLM data and cannot brute force, crack, or pass a password. This mechanism adds a new level of protection for enterprises without any requirement to entirely disable NTLM usage in the OS. You will be able to configure this option with Group Policy and PowerShell including blocking NTLM usage in SMB connections on demand with NET USE and PowerShell.

After the installation of Windows 11 Insider Preview Build 25951, the SMB Server provides support controlling SMB 2 and 3 dialects that it will negotiate. This technique changes legacy behavior where Windows SMB negotiates with the highest matched server dialect from SMB 2.0.2 to 3.1.1 clients. You should note that Windows 10 supports SMB client dialects controlling but not server dialects.

With the help of this option, an administrator can remove older SMB protocols from usage in the organization. It clocks older, less secure, and less capable Windows devices and third-party providers from connecting. You can configure this option with Group Policy and PowerShell. Moreover, both SMB client and server now include complete management support.

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The Windows 11 Insider Preview Build 25951 has adjusted the network flyout on the Lock screen. This is to match the UI of the network flyout from the system tray quick settings on the Taskbar. Microsoft has revealed that some of the popular games will not work correctly on the most recent Canary Channel Insider Preview Builds. The company has urged Windows Insiders to submit feedback in Feedback Hub. The problem associated with the print queue is under investigation.

The builds released to the Canary Channel are hot off the presses. The product team will provide documentation only if there are any new features or impactful known issues. However, you need not expect daily builds.

Anand Narayanaswamy is the editor-in-chief of Netans. He was recognized as a Microsoft Most Valuable Professional (MVP) for 9 years (2002 to 2011) and again as a Microsoft MVP in Surface under Windows and Devices in January 2024. He worked as a Chief Technical Editor with ASPAlliance and was part of ASPInsider program. Anand has published several articles and reviews related to various software and hardware products for various software and technology related websites. He is also active on social media and also participates as an Influencer for various brands. Anand can be reached at

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