Vulnerability Discussion

The system must disable account modification.

Account modification includes adding additional or modifying internet accounts in Apple Mail, Calendar, Contacts, in the Internet Account System Setting Pane, or the AppleID System Setting Pane.

This prevents the addition of unauthorized accounts.

[IMPORTANT]
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Some organizations may allow the use and configuration of the built-in Mail.app, Calendar.app, and Contacts.app for organizational communication. Information system security officers (ISSOs) may make the risk-based decision not to disable the Internet Accounts System Preference pane to avoid losing this functionality, but they are advised to first fully weigh the potential risks posed to their organization.
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Check

Verify the macOS system is configured to disable account modification with the following command:

/usr/bin/osascript -l JavaScript << EOS
$.NSUserDefaults.alloc.initWithSuiteName('com.apple.applicationaccess')\
.objectForKey('allowAccountModification').js
EOS

If the result is not "false", this is a finding.

Fix

Configure the macOS system to disable account modification by installing the "com.apple.applicationaccess" configuration profile.