S/Mime interoperability with external clients for message handling must be configured.
An XCCDF Rule
Description
<VulnDiscussion>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.</VulnDiscussion><FalsePositives></FalsePositives><FalseNegatives></FalseNegatives><Documentable>false</Documentable><Mitigations></Mitigations><SeverityOverrideGuidance></SeverityOverrideGuidance><PotentialImpacts></PotentialImpacts><ThirdPartyTools></ThirdPartyTools><MitigationControl></MitigationControl><Responsibility>System Administrator</Responsibility><Responsibility>Information Assurance Officer</Responsibility><IAControls></IAControls>
- ID
- SV-54003r1_rule
- Severity
- Medium
- References
- Updated
Remediation - Manual Procedure
Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "S/MIME interoperability with external clients" to "Enabled (Handle internally)".