Manual:$wgStrictFileExtensions

Uploads: $wgStrictFileExtensions
Toggle whether users may upload files not covered by $wgFileExtensions.
Introduced in version:	1.2.0
Removed in version:	still in use
Allowed values:	(boolean)
Default value:	true

Other settings: Alphabetical | By Function

Details

If set to true, users will only be able to upload files with proper extensions (see $wgFileExtensions).

If set to false, users will be able to upload files with almost any extension. A user attempting to upload a file whose extension is not in $wgFileExtensions will receive a warning message. However he may choose to ignore the message and upload the file anyway (assuming the file's extension is not in the $wgFileBlacklist).