Check: O365-OU-000016
Microsoft Office 365 ProPlus STIG:
O365-OU-000016
(in versions v3 r1 through v1 r2)
Title
The display of Level 1 attachments must be disabled in Outlook. (Cat II impact)
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". Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\16.0\outlook\security 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".
Additional Identifiers
Rule ID: SV-223361r961086_rule
Vulnerability ID: V-223361
Group Title: SRG-APP-000207
Expert Comments
CCIs
Number | Definition |
---|---|
CCI-001662 |
Take organization-defined corrective action when organization-defined unacceptable mobile code is identified. |
Controls
Number | Title |
---|---|
SC-18(1) |
Identify Unacceptable Code / Take Corrective Actions |