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The ability to demote attachments from Level 2 to Level 1 must be disabled.


Overview

Finding ID Version Rule ID IA Controls Severity
V-223360 O365-OU-000015 SV-223360r508019_rule Medium
Description
This policy setting controls whether Outlook users can demote attachments to Level 2 by using a registry key, which will allow them to save files to disk and open them from that location. Outlook uses two levels of security to restrict access to files attached to e-mail messages or other items. Files with specific extensions can be categorized as Level 1 (users cannot view the file) or Level 2 (users can open the file after saving it to disk). Users can freely open files of types that are not categorized as Level 1 or Level 2. If you enable this policy setting, users can create a list of Level 1 file types to demote to Level 2 by adding the file types to the following registry key: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security\Level1Remove. If you disable or do not configure this policy setting, users cannot demote level 1 attachments to level 2, and the HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security\Level1Remove registry key has no effect.
STIG Date
Microsoft Office 365 ProPlus Security Technical Implementation Guide 2022-06-17

Details

Check Text ( C-25033r442299_chk )
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Attachment Security >> Allow users to demote attachments to Level 2 is set to "Disabled".

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

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

If the value allowuserstolowerattachments is set to REG_DWORD = 0, this is not a finding.
Fix Text (F-25021r442300_fix)
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Attachment Security >> Allow users to demote attachments to Level 2 to "Disabled".