Send all signed messages as clear signed messages must be configured.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-17800	DTOO264	SV-54023r1_rule		Medium

Description
When users sign email messages with their signing certificate and send them, Outlook uses the sender's private key to encrypt the digital signature but sends the messages as clear text, unless they are encrypted separately. If users change this functionality by clearing the "Send clear text signed message when sending signed messages" option in the email Security section of the Trust Center, any recipients who are unable to access or use the sender's digital certificate will not be able to read the email messages.

Description

When users sign email messages with their signing certificate and send them, Outlook uses the sender's private key to encrypt the digital signature but sends the messages as clear text, unless they are encrypted separately. If users change this functionality by clearing the "Send clear text signed message when sending signed messages" option in the email Security section of the Trust Center, any recipients who are unable to access or use the sender's digital certificate will not be able to read the email messages.

STIG	Date
Microsoft Outlook 2013 STIG	2018-09-05

Details

Check Text ( C-47976r1_chk )
Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "Send all signed messages as clear signed messages" is set to "Enabled". Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\15.0\outlook\security Criteria: If the value ClearSign is REG_DWORD = 1, this is not a finding.

Check Text ( C-47976r1_chk )

Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "Send all signed messages as clear signed messages" is set to "Enabled".

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

HKCU\Software\Policies\Microsoft\Office\15.0\outlook\security

Criteria: If the value ClearSign is REG_DWORD = 1, this is not a finding.

Fix Text (F-46909r1_fix)
Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "Send all signed messages as clear signed messages" to "Enabled".