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2.5.14.3.1.3 Ensure 'Do not prompt about Level 1 attachments when closing an item' is set to 'Disabled'

Information

This policy setting controls whether Outlook displays a warning before closing an item that contains an unsafe attachment that will be blocked when the item is re-opened.

The recommended state for this setting is: Disabled.

Rationale:

To protect users from viruses and other harmful files, Outlook uses two levels of security, designated Level 1 and Level 2, to restrict users' access to files attached to e-mail messages or other items. Outlook completely blocks access to Level 1 files by default, and requires users to save Level 2 files to disk before opening them. Potentially harmful files can be classified into these two levels by file type extension, with all other file types considered safe.

By default, when a user closes an item to which a level 1 file has been attached, Outlook warns the user that the message contains a potentially unsafe attachment and that the user might not be able to access the attachment when opening the item later. (Such a sequence of events might occur when a user closes a draft message that they intend to resume editing at some future time.) If this configuration is changed, Outlook will not display the warning when the user closes the item but will still block the unsafe attachment if the user opens the message later. This functionality can cause users to lose access to important data.

Impact:

None - this is the default behavior.

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\Do not prompt about Level 1 attachments when closing an item

Default Value:

Disabled. (When a user closes an item to which a level 1 file has been attached, Outlook warns the user that the message contains a potentially unsafe attachment and that the user might not be able to access the attachment when opening the item later. (Such a sequence of events might occur when a user closes a draft message that they intend to resume editing at some future time.))

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: faea1ee656196224a00802f1ab11bf64ed63a2251bbe07ed50729c7218acda82