XWiki Platform is a generic wiki platform. Starting in version 14.3-rc-1,
org.xwiki.store.script.TemporaryAttachmentsScriptService#uploadTemporaryAttachment returns an instance of
com.xpn.xwiki.doc.XWikiAttachment. This class is not supported to be exposed to users without the
com.xpn.xwiki.api.Attachment should be used instead and takes case of checking the user's rights before performing dangerous operations. This has been patched in versions 14.9-rc-1 and 14.4.6. There are no known workarounds for this issue.