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. Rationale: 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 may not exist by default. It 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 Default Value: Windows 10 R1703 and older: Enabled. (The SMB client will allow insecure guest logons.) Windows 10 R1709 and newer: Disabled. (The SMB client will reject insecure guest logons.) CIS Controls: Version 6 9.1 Limit Open Ports, Protocols, and Services Ensure that only ports, protocols, and services with validated business needs are running on each system. Version 7 9.2 Ensure Only Approved Ports, Protocols and Services Are Running Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.