Manual:$wgAllowJavaUploads

Files and file uploads: $wgAllowJavaUploads
Allow Java archive uploads.
Introduced in version:1.18.0 (r82783)
Removed in version:1.39.0 (Gerrit change 788451; git #910d1466)
Allowed values:(boolean)
Default value:false

Details

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Allow Java archive uploads. This is not recommended for public wikis since a maliciously-constructed applet running on the same domain as the wiki can steal the user's cookies.

Allow uploading JAR files after 1.39.0

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MediaWiki version:
1.39

To retain the ability to allow uploading JAR files, remove application/java from $wgMimeTypeExclusions .