XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. In affected versions it's possible for a user to execute any content with the right of an existing document's content author, provided the user have edit right on it. A crafted URL of the form
/xwiki/bin/edit//?content=%7B%7Bgroovy%7D%7Dprintln%28%22Hello+from+ Groovy%21%22%29%7B%7B%2Fgroovy%7D%7D&xpage=view can be used to execute arbitrary groovy code on the server. This vulnerability has been patched in XWiki versions 14.10.6 and 15.2RC1. Users are advised to update. There are no known workarounds for this issue.