Title

Send all signed messages as clear signed messages must be configured. (Cat II impact)

Discussion

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.

Check Content

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

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

Additional Identifiers

Rule ID: SV-54023r1_rule

Vulnerability ID: V-17800

Group Title: DTOO264 - Clear signed messages

Expert Comments

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