2.5.14.3.1.2 Ensure 'Display Level 1 attachments' is set to 'Disabled'

Information

This policy setting controls whether Outlook blocks potentially dangerous attachments designated Level 1. To protect users from viruses and other harmful files, Outlook uses two levels of security, designated Level 1 and Level 2, to restrict access to files attached to e-mail messages or other items. Potentially harmful files can be classified into these two levels by file type extension, with all other file types considered safe.

The recommended state for this setting is: Disabled.

Rationale:

By default, Outlook completely blocks access to Level 1 files, and requires users to save Level 2 files to disk before opening them. If this configuration is changed, users will be able to open and execute potentially dangerous attachments, which can affect their computers or compromise the confidentiality, integrity, or availability of data.

Impact:

See attachment file types restricted by Office for the full list of file types classified Level 1 by default.

Important: For this setting to apply, the Outlook Security Mode setting must be enabled in User Configuration\Administrative Templates\Microsoft Outlook 2016\Security\Security with Use Outlook Security Group Policy selected, as set in this benchmark in Section 2.5.14.3.

Solution

To establish the recommended configuration via GP, set the following UI path to Disabled:

User Configuration\Administrative Templates\Microsoft Outlook 2016\Security\Security Form Settings\Attachment Security\Display Level 1 attachments

Default Value:

Disabled. (Outlook completely blocks access to Level 1 files, and requires users to save Level 2 files to disk before opening them.)

See Also

https://workbench.cisecurity.org/benchmarks/12129

Item Details

Category: SYSTEM AND INFORMATION INTEGRITY

References: 800-53|SI-3, 800-53|SI-8

Plugin: Windows

Control ID: 29494ef90ffe26ffbb5bfe01c5928a172626742eb1e914f22e56db413ebc7314