V-223360
SV-223360r961086_rule
CAT II
The ability to demote attachments from Level 2 to Level 1 must be disabled.
From: Microsoft Office 365 ProPlus Security Technical Implementation Guide (V3R5)
Description
<VulnDiscussion>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.</VulnDiscussion><FalsePositives></FalsePositives><FalseNegatives></FalseNegatives><Documentable>false</Documentable><Mitigations></Mitigations><SeverityOverrideGuidance></SeverityOverrideGuidance><PotentialImpacts></PotentialImpacts><ThirdPartyTools></ThirdPartyTools><MitigationControl></MitigationControl><Responsibility></Responsibility><IAControls></IAControls>
Check Procedure
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
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".
CCI Reference
CCI-001662- Created
- 2026-01-14 17:55:45
- Last Updated
- 2026-04-07 20:09:05