The macOS system must be configured with dedicated user accounts to decrypt the hard disk upon startup.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230762	APPL-11-000032	SV-230762r599842_rule		Medium

Description
When "FileVault" and Multifactor Authentication are configured on the operating system, a dedicated user must be configured to ensure that the implemented Multifactor Authentication rules are enforced. If a dedicated user is not configured to decrypt the hard disk upon startup, the system will allow a user to bypass Multifactor Authentication rules during initial startup and first login.

STIG	Date
Apple macOS 11 (Big Sur) Security Technical Implementation Guide	2020-11-27

Details

Check Text ( C-33707r591408_chk )
Retrieve a list of authorized FileVault users: # sudo fdesetup list fvuser,85F41F44-22B3-6CB7-85A1-BCC2EA2B887A If any unauthorized users are listed, this is a finding. Verify that the authorized FileVault users are marked as “DisabledUser”, preventing console logins: Note: This procedure will need to be run for each authorized FileVault User. # sudo dscl . read /Users/ AuthenticationAuthority \| grep "DisabledUser" AuthenticationAuthority: ;ShadowHash;HASHLIST: ;Kerberosv5;;unlock@LKDC:SHA1.20BABA05A6B1A86A8C57581A8487596640A3E37B;LKDC:SHA1.20CEBE04A5B1D92D8C58189D8487593350D3A40A; ;SecureToken; DisabledUser If the FileVault user is not disabled, this is a finding.

Check Text ( C-33707r591408_chk )

Retrieve a list of authorized FileVault users:

# sudo fdesetup list

fvuser,85F41F44-22B3-6CB7-85A1-BCC2EA2B887A

If any unauthorized users are listed, this is a finding.

Verify that the authorized FileVault users are marked as “DisabledUser”, preventing console logins:

Note: This procedure will need to be run for each authorized FileVault User.

# sudo dscl . read /Users/ AuthenticationAuthority | grep "DisabledUser"

AuthenticationAuthority: ;ShadowHash;HASHLIST: ;Kerberosv5;;unlock@LKDC:SHA1.20BABA05A6B1A86A8C57581A8487596640A3E37B;LKDC:SHA1.20CEBE04A5B1D92D8C58189D8487593350D3A40A; ;SecureToken; DisabledUser

If the FileVault user is not disabled, this is a finding.

Fix Text (F-33680r592242_fix)
Create an authorized user account that will be used to unlock the disk on startup. Disable the login ability of the newly created user account: # sudo dscl . append /Users/ AuthenticationAuthority DisabledUser Remove all FileVault login access from each user account defined on the system that is not a designated FileVault user: # sudo fdesetup remove -user