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Trust Bar notification must be enabled for unsigned application add-ins in Excel and blocked.


Overview

Finding ID Version Rule ID IA Controls Severity
V-223337 O365-EX-000028 SV-223337r508019_rule Medium
Description
This policy setting controls whether the specified Office 2016 applications notify users when unsigned application add-ins are loaded or silently disable such add-ins without notification. This policy setting only applies if you enable the ''Require that application add-ins are signed by Trusted Publisher'' policy setting, which prevents users from changing this policy setting. If you enable this policy setting, applications automatically disable unsigned add-ins without informing users. If you disable this policy setting, if an application is configured to require that all add-ins be signed by a trusted publisher, any unsigned add-ins the application loads will be disabled and the application will display the Trust Bar at the top of the active window. The Trust Bar contains a message that informs users about the unsigned add-in. If you do not configure this policy setting, the disable behavior applies, and in addition, users can configure this requirement themselves in the ''Add-ins'' category of the Trust Center for the application.
STIG Date
Microsoft Office 365 ProPlus Security Technical Implementation Guide 2022-06-17

Details

Check Text ( C-25010r442230_chk )
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Excel 2016 >> Excel Options >> Security >> Trust Center >> Disable Trust Bar Notification for unsigned application add-ins and block them is set to "Enabled".

Use the Windows Registry Editor to navigate to the following key:

HKCU\software\policies\microsoft\office\16.0\excel\security

If the value for notbpromptunsignedaddin is REG_DWORD = 1, this is not a finding.
Fix Text (F-24998r442231_fix)
Set policy value for User Configuration >> Administrative Templates >> Microsoft Excel 2016 >> Excel Options >> Security >> Trust Center >> Disable Trust Bar Notification for unsigned application add-ins and block them to "Enabled".