Hidden Users
Where this stands
One published detection covers this technique. Every one is unverified — no rule on Siemphony has been executed against real telemetry.
What the technique is
Adversaries may use hidden users to hide the presence of user accounts they create or modify. Administrators may want to hide users when there are many user accounts on a given system or if they want to hide their administrative or other management accounts from other users. In macOS, adversaries can create or modify a user to be hidden through manipulating plist files, folder attributes, and user attributes. To prevent a user from being shown on the login screen and in System Preferences, adversaries can set the userID to be under 500 and set the key value Hide500Users to TRUE in the /Library/Preferences/com.apple.loginwindow plist file. Every user has a userID associated with it. When the Hide500Users key value is set to TRUE, users with a userID under 500 do not appear on the login screen and in System Preferences. Using the command line, adversaries can use the dscl utility to create hidden user accounts by setting the IsHidden attribute to 1. Adversaries can also hide a user’s home folder by changing the chflags to hidden. Adversaries may similarly hide user accounts in Windows. Adversaries can set the HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList Registry key value to 0 for a specific user to prevent that user from being listed on the logon screen. […]
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN1001
Registry modifications to HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList setting user visibility to 0, or creation of user accounts not shown on login screen. Defender view: correlation of account creation with registry edits that mark users hidden.
- AN1002
Use of gsettings or direct Display Manager modifications to hide users from greeter login screen. Defender view: anomalous command execution modifying org.gnome.login-screen or other greeter configurations.
- AN1003
User creation or modification via dscl with IsHidden=1, UID<500, or plist edits to com.apple.loginwindow Hide500Users flag. Defender view: correlation of hidden account attributes with login screen exclusion.
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