Manual:$wgTrustedMediaFormats

Details
List of trusted media-types and mime types. Use the MEDIATYPE_xxx constants to represent media types. This list is used by Image::isSafeFile

MIME types not listed here will have the content of the system message MediaWiki:Mediawarning displayed on the images description page. The default message is: Warning: This file may contain malicious code, by executing it your system may be compromised. It would also be possible to use this for further restrictions, like disabling direct [[media:...]] links for non-trusted formats.