The ability to display level 1 attachments must be disallowed.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-228440 | DTOO240 | SV-228440r508021_rule | CCI-001662 | medium |
| Description | ||||
| 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. | ||||
| STIG | Date | |||
| Microsoft Outlook 2016 Security Technical Implementation Guide | 2022-03-11 | |||
Details
Check Text (C-228440r508021_chk)
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 (F-30658r497643_fix)
Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Security Form Settings -> Attachment Security "Display Level 1 attachments" to "Disabled".