2.4.3 Ensure Screen Sharing Is Disabled

Information

Screen Sharing allows a computer to connect to another computer on a network and display the computer's screen. While sharing the computer's screen, the user can control what happens on that computer, such as opening documents or applications, opening, moving, or closing windows, and even shutting down the computer.

While mature administration and management does not use graphical connections for standard maintenance, most help desks have capabilities to assist users in performing their work when they have technical issues and need support. Help desks use graphical remote tools to understand what the user sees and assist them so they can get back to work. For MacOS, some of these remote capabilities can use Apple's OS tools. Control is therefore not meant to prohibit the use of a just-in-time graphical view from authorized personnel with authentication controls. Sharing should not be enabled except in narrow windows when help desk support is required.

Rationale:

Disabling Screen Sharing mitigates the risk of remote connections being made without the user of the console knowing that they are sharing the computer.

Impact:

Help desks may require the periodic use of a graphical connection mechanism to assist users. Any support that relies on native MacOS components will not work unless a scripted solution to enable and disable sharing as neccessary.

Solution

Perform the following to disable Screen Sharing:
Graphical Method:

Open System Preferences

Select Sharing

Uncheck Screen Sharing

Terminal Method:
Run the following command to turn off Screen Sharing:

$ sudo launchctl disable system/com.apple.screensharing

See Also

https://workbench.cisecurity.org/files/4000