Information
This policy setting determines if the SMB client will allow insecure guest logons to an SMB server.
The recommended state for this setting is: Disabled
Insecure guest logons are used by file servers to allow unauthenticated access to shared folders.
Solution
To establish the recommended configuration via GP, set the following UI path to Disabled:
Computer Configuration\Policies\Administrative Templates\Network\Lanman Workstation\Enable insecure guest logons
Note: This Group Policy path is provided by the Group Policy template LanmanWorkstation.admx/adml that is included with the Microsoft Windows 10 Release 1511 Administrative Templates (or newer).
Impact:
The SMB client will reject insecure guest logons. This was not originally the default behavior in older versions of Windows, but Microsoft changed the default behavior starting with Windows 10 R1709:
Guest access in SMB2 disabled by default in Windows 10 and Windows Server 2016