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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-230762r802378_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 2022-02-16

Details

Check Text ( C-33707r802376_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 shell for authorized FileVault users is set to “/usr/bin/false”, which prevents console logins:
$ sudo dscl . read /Users/ UserShell

UserShell: /usr/bin/false

If the FileVault users' shell is not set to "/usr/bin/false", this is a finding.
Fix Text (F-33680r802377_fix)
Note: In previous versions of macOS, this setting was implemented differently. Systems that used the previous method should prepare the system for the new method by creating a new unlock user, verifying its ability to unlock FileVault after reboot, then deleting the old FileVault unlock user.

Disable the login ability of the newly created user account:
$ sudo /usr/bin/dscl . change /Users/ UserShell /usr/bin/false

Remove all FileVault login access from each user account defined on the system that is not a designated FileVault user:
$ sudo fdesetup remove -user