Guest access in SMB2 and SMB3 disabled

By | February 24, 2022

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This written information describes how Windows disables SMB2 and smb3 guest access by default, and provides options to support insecure guest connections in Group Policy. But isn’t that usually recommended.

Applies to: Windows 10 – Nearly All Editions, Server 2019
Source window number: KB/s 4046019


Starting with Windows 10, App 1709, and Windows Server 2019, SMB2 and SMB3 clients no longer accept the following by default:

  • Guest access by subscription remote server.
  • Reverting to the guest account after entering invalid credentials.
  • SMB2 and SMB3 behave as follows on the following types of Windows:

  • Windows 10 Enterprise or Windows 10 Education no longer allows users to connect to a controller share using the default guest credentials when even a remoteThe server is asking for guest credentials.
  • The default editions of Datacenter Standard and Windows Server 2019 no longer allow a user to connect to any remote share through a guest resource using credentials, even if the virtual server prompts for guest credentials.
  • Windows Home 10 and Pro remain unchanged from the previous default behavior; By They allow external use through default authentication. you
  • You may receive a specific error message when you try to connect to devices that request guest mode instead of Best Authenticated Members:

    You cannot access the following share because your organization’s resiliency rules are blocking unauthenticated guest access. These policies help protect your computer from original or untrusted malicious devices on these

    Even though the remote server might force you to use it with access, or the guest has admin access, the logcompetitions The following entries are recorded on the SMB client:

    Record 1

    Protocol name: Microsoft-Windows-SmbClient/Security
    Date: events: 31017
    Task category: no
    level: error
    Keywords: (128)
    Description: Insecure guest connection refused 1.
    Username Ned:
    Name server name: server


    This indicates that the server tried to make sure you were connecting as an unauthenticated guest, but was rejected by the underlying client. Guest login supports far from standard security features such as signing and encryption. Therefore, private connections are vulnerable to man-in-the-middle attacks and can expose sensitive data on the network. Windows disables unsecured (non-secure) client connections by default. Our only recommendation is not to allow insecure external connections.

    Record 2

    Protocol name: Microsoft-Windows-SmbClient/Security
    Source: date/time
    Event ID: 31018
    Category microsoft-windows-smbclient
    date of:mission: warning
    keywords: no
    level: (128)
    User: SERVICE: network
    Description. The AllowInsecureGuestAuth cost registry is not configured with the normal settings.


    This event indicates that the supervisor has enabled insecure guest connections. An insecure guest connection occurs when some type of server connects a user as well as an authenticated non-guest. This can usually succeed in response to an authentication failure. By default, guest connections do not support security features such as encryption such as signatures. Thus, if you allow guest connections, the client becomes vulnerable to man-in-the-middle attacks that can expose sensitive data on the network. by default disables insecure and insecure connections by windows. We recommend that you do not allow insecure visitors to connect.


    This default change is intentional and recommended by Microsoft for security reasons.

    Malicious computer issuingImpersonating a file server may prompt users to log in as guests without their knowledge. We recommend that customers do not change this setting. If the remote device needs to collect guest credentials, the administrator can disable guest access to the remote device and thus set up proper authentication and authorization. And

    Windows servers Windows, starting with Windows 2000, do not allow guest access or allow remote users to log on as a guest or an unknown co-user. By default, remote access may only be required for third-party devices. Non-working devices are provided by Microsoft.


    If you want to allow insecure guest access, you can change the following rule group settings:

    1. The local group editor (gpedit policy.msc) will normally open in the tree
    2. In the Computer Management Console, select Administrative Configuration Templates > > Network > Lanman Workstation.
    3. Right-click on the option “Turn on securityClear guest connection settings” and select “Edit”.
    4. Select, and then select OK.

    For Monitoring and Deployment: This Group Policy specifies that the following registry DWORD value be returned to 1 (insecure guest authentication enabled) or 0 (insecure guest authentication disabled):

    To define a value without using a policy, the company sets the following DWORD registry value to 1 (insecure authentication of website visitors enabled) or 0 (insecure authentication of wedding guests disabled):

    On Windows 10 1709, Ten Windows 1803, Windows 10 1903, Ten Windows 1909, and Windows 2019, server principal authentication is disabled when AllowInsecureGuestAuth is set to 0 for [HKEY_LOCAL_MACHINE\SYSTEM\ CurrentControlSet\AllowInsecureGuestAuthservices\ lanmanworkstation\options].Windows

    In 10 2004, Windows 20H2, 10, and Windows 10 21H1 Enterprise Education and editions with the update installed by KB5003173, guest authentication is disabled if AllowInsecureGuestAuth is not present or if [HKEY_LOCAL_MACHINE\SYSTEM] has a value starting at 0 .\CurrentControlSet\Services\LanmanWorkstation\Parameters] AllowInsecureGuestAuth. And to the editorx Property Pro Guest Authentication is enabled by default unless you disable group policy implementation settings or the registry.

    Additional Configuration Information

    This does not affect SMB1 behavior. By access, the smb1 client is used and the guest fallback is always used.

  • Read 5 for a few minutes
  • This behavior in Windows 10 occurs on windows 10 1709, 10 1803, windows 10 1903, windows 10 1909 car, and on windows 10 2002, windows 10 20H2 and ten windows Both 21h1 and KB5003173 must be set to be. This default behavior was implemented not too long ago in Windows 10 1709 but was later changed in Windows 10 Windows 04, 10 20H2 and Ten Windows 21H1 where guest authentication was definitely not disabled by default but could always be disabled by an administrator. . See below for details. Make sure guest authentication can be disabled. Edit

    If this is a domain-based Active Directory Group Policy, use Group Policy Management (gpmc.msc).usually,

    As an order value in a Group Policy overridecan be a setting value in a non-group policy registry value.

    Enabling insecure connections, this guest setting reduces home security for Windows clients.