XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Simple users can create global SSX/JSX without specific rights: in theory only users with Programming Rights should be allowed to create SSX or JSX that are executed everywhere on a wiki. But a bug allow anyone with edit rights to actually create those. This issue has been patched in XWiki 13.10-rc-1, 12.10.11 and 13.4.6. There's no easy workaround for this issue, administrators should upgrade their wiki.
