The default message format must be set to use Plain Text.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-251866	DTOO314	SV-251866r811197_rule		Medium

Description
Outlook uses HTML as the default email format. HTML format poses a security risk by embedding information into the email itself, which could allow for release of sensitive information. If a user attempted to insert an HTML link into an email message, the link itself may direct to a malicious website. By sending emails in HTML format, the recipient could be subject to becoming infected by the malicious website.

Description

Outlook uses HTML as the default email format. HTML format poses a security risk by embedding information into the email itself, which could allow for release of sensitive information. If a user attempted to insert an HTML link into an email message, the link itself may direct to a malicious website. By sending emails in HTML format, the recipient could be subject to becoming infected by the malicious website.

STIG	Date
Microsoft Outlook 2016 Security Technical Implementation Guide	2022-03-11

Details

Check Text ( C-55326r811187_chk )
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Mail Format >> Internet Formatting >> Message Format "Set message format" is "Enabled: Plain Text". Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\16.0\outlook\options\mail Criteria: If the value EditorPreference is REG_DWORD = 65536 (dec), this is not a finding.

Check Text ( C-55326r811187_chk )

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Mail Format >> Internet Formatting >> Message Format "Set message format" is "Enabled: Plain Text".

Procedure: Use the Windows Registry Editor to navigate to the following key:

HKCU\Software\Policies\Microsoft\Office\16.0\outlook\options\mail

Criteria: If the value EditorPreference is REG_DWORD = 65536 (dec), this is not a finding.

Fix Text (F-55280r811188_fix)
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Mail Format >> Internet Formatting >> Message Format "Set message format" to "Enabled: Plain Text".