S/Mime interoperability with external clients for message handling must be configured.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-17790	DTOO257	SV-54003r1_rule		Medium

Description
In some situations, administrators might wish to use an external program, such as an add-in, to handle S/MIME message decryption. If your organization works with encrypted messages that the decryption functionality in Outlook cannot handle appropriately, this setting can be used to configure Outlook to hand S/MIME messages off to an external program for decryption. If no external program has been authorized however, misconfiguring this setting could allow unauthorized and potentially dangerous programs to handle encrypted messages, which could compromise security.

Description

In some situations, administrators might wish to use an external program, such as an add-in, to handle S/MIME message decryption. If your organization works with encrypted messages that the decryption functionality in Outlook cannot handle appropriately, this setting can be used to configure Outlook to hand S/MIME messages off to an external program for decryption. If no external program has been authorized however, misconfiguring this setting could allow unauthorized and potentially dangerous programs to handle encrypted messages, which could compromise security.

STIG	Date
Microsoft Outlook 2013 STIG	2018-09-05

Details

Check Text ( C-47973r1_chk )
Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "S/MIME interoperability with external clients" is set to "Enabled (Handle internally)". 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 ExternalSMime is REG_DWORD = 0, this is not a finding.

Check Text ( C-47973r1_chk )

Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "S/MIME interoperability with external clients" is set to "Enabled (Handle internally)".

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 ExternalSMime is REG_DWORD = 0, this is not a finding.

Fix Text (F-46892r1_fix)
Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "S/MIME interoperability with external clients" to "Enabled (Handle internally)".