SMB NTLM blocking
Microsoft's edit ·
Microsoft's commit message in MicrosoftDocs/windowsserverdocs · commit 9777819 · +3 −3 lines · also on GitHub
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---
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−title: Block NTLM connections on SMB (preview)
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+title: Block NTLM connections on SMB in Windows Server 2025 (Preview)
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description: Learn how to make SMB more secure by blocking NTLM.
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ms.topic: how-to
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author: Heidilohr
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# Block NTLM connections on SMB (preview)
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> [!IMPORTANT]
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−> Windows Server Insider builds are in PREVIEW.
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+> Windows Server 2025 (Preview) is in PREVIEW.
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> This information relates to a prerelease product that may be substantially modified before it's released. Microsoft makes no warranties, expressed or implied, with respect to the information provided here.
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The SMB client now supports blocking NTLM authentication for remote outbound connections. Blocking NTLM authentication prevents bad actors from tricking clients into sending NTLM requests to malicious servers, counteracting brute force, cracking, and pass-the-hash attacks. NTLM blocking is also required for switching an organization's authentication protocols to Kerberos, which is more secure than NTLM because it can verify server identities with its ticket system. However, organizations can also enable this layer of protection without having to disable NTLM entirely.
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## Configure SMB client NTLM blocking
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−Starting with Windows Server Insiders build 25951 and Windows 11 Insiders build 25951, you have the option to configure SMB to block NTLM. To improve the security of deployments running earlier versions of Windows, you must disable NTLM manually, either by editing the relevant Group Policy or running a specific command in PowerShell.
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+Starting with Windows Server 2025 (Preview) and Windows 11 Insiders build 25951, you have the option to configure SMB to block NTLM. To improve the security of deployments running earlier versions of Windows, you must disable NTLM manually, either by editing the relevant Group Policy or running a specific command in PowerShell.
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To configure NTLM blocking:
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Microsoft's Markdown source from MicrosoftDocs/windowsserverdocs, © Microsoft Corporation, under CC BY 4.0. Changed lines with up to 3 unchanged lines around each; ChangeIntel kept this copy 10 Oct 08:53 UTC. The commit date is when the source changed, which can be hours or days before Learn published it.