OSX apple remote desktop

Wed 16 December 2020

Some commands that can be useful when you need to activate remote desktop from the commandline osx.

The kickstart utility

MacOS come with a script called kickstart that you can use to enable all sorts of feature regarding remote-control of your mac. First step is to check the documentation page.

% sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -help | less

alternatively: https://ss64.com/osx/kickstart.html

Be careful and understand the different option before you enable anything. You do not want to open your computer too much, or to the wrong people.

% sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -activate -configure -allowAccessFor -specifiedUsers
Starting...
Warning: macos 10.14 and later only allows control if Screen Sharing is enabled through System Preferences.
Activated Remote Management.
Setting allow all users to NO.
Done.
% sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -configure -users a_user -access -on -privs -all
Starting...
a_user: Set user remote control privileges.
a_user: Set user remote access.
Done.

Which translate to: * Activate ARD and configure it to only grant access to users whom we have given some privileges. * Grant the user "ausername" some privileges, in this example we grant access on + privileges all.

PS: The activate part also set ARD to start on boot, so you are making it persistent.

If you do not want to grant all privileges you can choose something else:

-configure -privs -all             ## Grant all privileges (default)
-configure -privs -none            ## Disable all privileges for specified user
-configure -privs -DeleteFiles
-configure -privs -ControlObserve  ## Control AND observe (unless ObserveOnly is also specified)
-configure -privs -TextMessages    ## Send a text message
-configure -privs -ShowObserve     ## Show client when being observed or controlled
-configure -privs -OpenQuitApps    ## Open and quit applications
-configure -privs -GenerateReports ## Generate reports (and search hard drive)
-configure -privs -RestartShutDown
-configure -privs -SendFiles       ## Send *and/or* retrieve files
-configure -privs -ChangeSettings  ## Change system settings
-configure -privs -ObserveOnly     ## Modify ControlObserve option to allow Observe mode only
-configure -privs -mask mask_no    ## Specify "naprivs" mask numerically instead (advanced)

I also recommend to turn off ARD when you are done with it:

% sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -deactivate -stop -configure -access -off
Starting...
Removed preference to start ARD after reboot.
a_user: Set user remote access.
b_user: Set user remote access.
Done.

Which translate to: * Stop the Remote Management service and deactivate it so it will not start after the next computer restart. * Disable remote access for a_user and b_user (and other user that might exist on your macos system).

Here it how the GUI (system preferences -> sharing) will respond to the commands:

A brief look into the security aspect

I have tried to do some information gathering about the security around this.

The first step is to read the official documentation: https://support.apple.com/no-no/guide/remote-desktop/welcome/mac

When using Control or Observe to access a Mac using the Screen Sharing or Remote Management service, all data is encrypted for transit using the AES with a 128-bit shared key that was derived during screen sharing authentication.

ref: https://support.apple.com/no-no/guide/remote-desktop/apdfe8e386b/3.9.4/mac/10.15.6

When connecting to an remote-desktop we can also look at the network traffic to get a clue of what is going on.

First, we are presented with 4 different types of security, where one is a proprietary Apple Remote Desktop type:

Next, we can see that it ends up choosing a security type of tls:

The last step, negotation of ciphers to use:

... where we can extract the following information:

Pmda=SHA-512,replay_detection,conf+int=ChaCha20-Poly1305,kdf=SALTED-SHA512-PBKDF2

So it seems that it does some kind of TLS security for our traffic, which is good.

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