Information
This policy setting determines whether Internet Explorer MIME sniffing will prevent promotion of a file of one type to a more dangerous file type.
If you enable this policy setting, MIME sniffing will never promote a file of one type to a more dangerous file type.
If you disable this policy setting, Internet Explorer processes will allow a MIME sniff promoting a file of one type to a more dangerous file type.
If you do not configure this policy setting, MIME sniffing will never promote a file of one type to a more dangerous file type.
Solution
Policy Path: Windows Components\Internet Explorer\Security Features\Mime Sniffing Safety Feature
Policy Setting Name: Internet Explorer Processes