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

From Microsoft Outlook 2010

Part of DTOO257 - No S/Mime interop w/ external clients

SV-33566r1_rule S/Mime interoperability with external clients for message handling must be configured.

Vulnerability discussion

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.

Check content

The policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2010 -> Security -> Cryptography “S/MIME interoperability with external clients” must be set to “Enabled (Handle internally)”. Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\14.0\outlook\security Criteria: If the value ExternalSMime is REG_DWORD = 0, this is not a finding.

Fix text

Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2010 -> Security -> Cryptography “S/MIME interoperability with external clients” to “Enabled (Handle internally)”.

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