Manual:$wgFileBlacklist

Details
Files with these extensions will never be allowed as uploads if $wgCheckFileExtensions is set to true.

$wgFileBlacklist overrides $wgFileExtensions, so you must remove an extension from the blacklist before you can upload files that have it. For instance, to allow users to upload executables, add this to LocalSettings.php:

History

 * 'cgi' was added in 1.3.8
 * 'js' and 'jsb' were added in 1.5.0
 * 'php5' was added in 1.8.0