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

Overview

Finding IDVersionRule IDIA ControlsSeverity
V-223360O365-OU-000015SV-223360r961086_ruleCCI-001662medium
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.
STIGDate
Microsoft Office 365 ProPlus Security Technical Implementation Guide2025-03-05

Related Frameworks

1 mapping across 4 frameworks
SCF0 mappings

No source states a mapping between these directly.

Also reachable in 3 hops (3) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

END-10Mobile Code
0.50
VPM-02Vulnerability Remediation Process
0.50
VPM-04Continuous Vulnerability Remediation Activities
0.50
NIST 800-530 mappings

No source states a mapping between these directly.

Also reachable in 2 hops (4) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

CM-7Least Functionality
1.00
SC-18(1)Identify Unacceptable Code and Take Corrective Actions
1.00
SC-18(3)Prevent Downloading and Execution
1.00
SC-18(4)Prevent Automatic Execution
1.00
CCI1 mapping
CCI-001662
1.00
NIST CSF 2.00 mappings

No source states a mapping between these directly.

Also reachable in 4 hops (2) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

ID.RA-08
0.50
PR.PS-02
0.50

Details

Check Text (C-223360r961086_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".