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

From Microsoft Outlook 2016 Security Technical Implementation Guide

Associated with: CCI-000366

SV-85855r1_rule Send all signed messages as clear signed messages must be configured.

Vulnerability discussion

This policy setting controls whether Outlook sends signed messages as clear text signed messages. If you enable this policy setting, the "Send clear text signed message when sending signed messages" option is selected in the E-mail Security section of the Trust Center. If you disable or do not configure this policy setting, when users sign e-mail messages with their digital signature and send them, Outlook uses the signature's private key to encrypt the digital signature but sends the messages as clear text, unless they are encrypted separately.

Check content

Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2016 -> 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\16.0\outlook\security Criteria: If the value ClearSign is REG_DWORD = 1, this is not a finding.

Fix text

Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Cryptography "Send all signed messages as clear signed messages" to "Enabled".

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