Beyond the good ol' LaunchAgents - 27 - Dock shortcuts

This is part 27 in the series of “Beyond the good ol’ LaunchAgents”, where I try to collect various persistence techniques for macOS. For more background check the introduction.

This persistence is another gem I found in Leo Pitt’s Modern macOS Persistence talk.

macOS Dock stores shortcuts for applications, that we would like to access through the, well… Dock. It stores all settings in ~/Library/Preferences/com.apple.dock.plist. Although we can edit this PLIST directly, we can also use the defaults utility to change it. For example adding a new entry:

defaults write com.apple.dock persistent-apps -array-add '<dict><key>tile-data</key><dict><key>file-data</key><dict><key>_CFURLString</key><string>/System/Applications/Books.app</string><key>_CFURLStringType</key><integer>0</integer></dict></dict></dict>'

killall Dock

This is part 27 in the series of “Beyond the good ol’ LaunchAgents”, where I try to collect various persistence techniques for macOS. For more background check the introduction.

Note that we don’t need to add the bundle-identifier or the book tags, what is also detailed in Leo’s presentation.

At the end we need to restart Dock, so the new icon shows up. Of course we could also change items. The problem it creates is that defaults uses the cfprefsd daemon to change the file, which is the one that normally changes this file anyway, so this can break detection. Below is the fs_usage file system log showing this change.

14:51:53  openat            [3]/com.apple.dock.plist                                                         0.000017   cfprefsd    
14:51:53  openat            [3]/com.apple.dock.plist                                                         0.000010   cfprefsd    
14:51:53  openat            [3]/com.apple.dock.plist                                                         0.000008   cfprefsd    
14:51:53    RdData[A]       com.apple.dock.plist                                                             0.000822 W cfprefsd    
14:51:53  openat            [3]/com.apple.dock.plist                                                         0.000012   cfprefsd    
14:51:53  fstatat64         [3]/com.apple.dock.plist                                                         0.000006   cfprefsd    
14:51:53  openat            [3]/com.apple.dock.plist                                                         0.000012   cfprefsd    
14:51:53  access            /Users/csaby/Library/Preferences/com.apple.dock.plist                            0.000011   cfprefsd    
14:51:53  openat            /_hwnkhn904xg_pwlhb83_k040000gn/T/TemporaryItems/com.apple.dock.plist.I5zYdrH    0.000127   cfprefsd    
14:51:53    WrData[A]       /_hwnkhn904xg_pwlhb83_k040000gn/T/TemporaryItems/com.apple.dock.plist.I5zYdrH    0.000154 W cfprefsd 

The other thing we can do, if we don’t want to rely on defaults, is calling the Preferences API directly to change the file, or even cfprefsd’s XPC service. Thus as an attacker we can mask the change of this file to appear as legitimate. I leave this as an exercise to the reader how to do these.

macOS admins work a lot with Dock preferences, so you can find other tricks in their blogposts, here are a few for example:

Adding Objects To The Dock - krypted Terminal Tricks: Mastering the Iconic macOS Dock, Part 3 GitHub - kcrawford/dockutil: command line tool for managing dock items