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Level 1 file attachments must be blocked from being delivered.

Overview

Finding IDVersionRule IDIA ControlsSeverity
V-223362O365-OU-000017SV-223362r961086_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 email 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\16.0\Outlook\Security\Level1Remove. If this policy setting is disabled or not configured, users cannot demote Level 1 attachments to Level 2, and the HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\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-223362r961086_chk)

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Attachment Security >> Remove file extensions blocked as Level 1 is set to "Disabled". Use the Windows Registry Editor to navigate to the following key: HKCU\software\policies\microsoft\office\16.0\outlook\security\FileExtensionsRemoveLevel1 If the registry key exists, this is a finding.

Fix Text (F-25023r442306_fix)

Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Attachment Security >> Remove file extensions blocked as Level 1 to "Disabled".