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1.13.1.3 Ensure 'Display pictures and external content in HTML e-mail' is set to Enabled

Information

This policy setting controls whether Outlook downloads untrusted pictures and external content located in HTML e-mail messages without users explicitly choosing to download them.
If you enable this policy setting, Outlook will not automatically download content from external servers unless the sender is included in the Safe Senders list. Recipients can choose to download external content from untrusted senders on a message-by-message basis.
If you disable this policy setting, Outlook does not display pictures and external content in HTML e-mail.
If you do not configure this policy setting, Outlook does not download external content in HTML e-mail and RSS items unless the content is considered safe. Content that Outlook can be configured to consider safe includes:

* Content in e-mail messages from senders and to recipients defined in the Safe Senders and Safe Recipients lists.
* Content from Web sites in Internet Explorer's Trusted Sites security zone.
* Content in RSS items.
* Content from SharePoint Discussion Boards. Users can control what content is considered safe by changing the options in the 'Automatic Download' section of the Trust Center.

If Outlook's default blocking configuration is overridden, in the Trust Center or by some other method, Outlook will display external content in all HTML e-mail messages, including any that include Web beacons. The recommended state for this setting is: Enabled.

Rationale:

Malicious e-mail senders can send HTML e-mail messages with embedded Web beacons, which are pictures and other content from external servers that can be used to track whether specific recipients open the message. Viewing an e-mail message that contains a Web beacon provides confirmation that the recipient's e-mail address is valid, which leaves the recipient vulnerable to additional spam and harmful e-mail.

By default, Outlook does not download external content in HTML e-mail and RSS items unless the content is considered safe. Content that Outlook can be configured to consider safe includes:

* Content in e-mail messages from senders and to recipients defined in the Safe Senders and Safe Recipients lists.
* Content from Web sites in Internet Explorer's Trusted Sites security zone.
* Content in RSS items.
* Content from SharePoint Discussion Boards.

Users can control what content is considered safe by changing the options in the Automatic Download section of the Trust Center. If Outlook's default blocking configuration is overridden, in the Trust Center or by some other method, Outlook will display external content in all HTML e-mail messages, including any that include Web beacons.

Solution

To implement the recommended configuration state, set the following Group Policy setting to Enabled.

User Configuration\Administrative Templates\Microsoft Outlook 2013\Security\Automatic Picture Download Settings\Display pictures and external content in HTML e-mail

Impact:

Enabling this setting enforces the default configuration in Outlook, and therefore is unlikely to cause usability issues for most users.

See Also

https://workbench.cisecurity.org/files/552

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-18(3)

Plugin: Windows

Control ID: 227c7de291983139b0d960e2ff5974f1d990f8e4868393bb7e6e298101758a61