The S/MIME specification allows a Cipher Block Chaining (CBC) malleability-gadget attack that can indirectly lead to plaintext exfiltration, aka EFAIL.
Microsoft Outlook 2007, Microsoft Outlook 2010, Microsoft Outlook 2013, Microsoft Outlook 2016, and Microsoft Office 2016 Click-to-Run allow an elevation of privilege vulnerability due to how the format of incoming message is validated, aka "Microsoft Outlook Elevation of Privilege Vulnerability".