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V-228440

CAT II (Medium)

The ability to display level 1 attachments must be disallowed.

Rule ID

SV-228440r961086_rule

STIG

Microsoft Outlook 2016 Security Technical Implementation Guide

Version

V2R4

CCIs

CCI-001662

Discussion

This policy setting controls whether Outlook blocks potentially dangerous attachments designated Level 1. Outlook uses two levels of security to restrict users' 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, Outlook users can gain access to Level 1 file type attachments by first saving the attachments to disk and then opening them, as with Level 2 attachments. If you disable this policy setting, Level 1 attachments do not display under any circumstances. If you do not configure this policy setting, Outlook completely blocks access to Level 1 files, and requires users to save Level 2 files to disk before opening them.

Check Content

Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Security Form Settings -> Attachment Security "Display Level 1 attachments" is set to "Disabled".

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

HKCU\Software\Policies\Microsoft\Office\16.0\outlook\security

Criteria: If the value ShowLevel1Attach is 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 "Display Level 1 attachments" to "Disabled".