Outlook must be configured to prevent users overriding attachment security settings.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-223353	O365-OU-000008	SV-223353r961353_rule		Medium

Description

This policy setting prevents users from overriding the set of attachments blocked by Outlook. If you enable this policy setting users will be prevented from overriding the set of attachments blocked by Outlook. Outlook also checks the "Level1Remove" registry key when this setting is specified. If you disable or do not configure this policy setting, users will be allowed to override the set of attachments blocked by Outlook.

STIG	Date
Microsoft Office 365 ProPlus Security Technical Implementation Guide	2025-03-05

Details

Check Text (C-25026r442278_chk)

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Prevent users from customizing attachment security settings is set to "Enabled".

Use the Windows Registry to navigate to the following key:

HKCU\software\policies\microsoft\office\16.0\outlook

If the value for disallowattachmentcustomization is set to REG_DWORD = 1, this is not a finding.

Fix Text (F-25014r442279_fix)

Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Prevent users from customizing attachment security settings to "Enabled".