XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Any guest can perform arbitrary remote code execution through a request to "SolrSearch". This impacts the confidentiality, integrity and availability of the whole XWiki installation. To reproduce on an instance, without being logged in, go to "<host>/xwiki/bin/get/Main/SolrSearch?media=rss&text=%7D%7D%7D%7B%7Basync%20async%3Dfalse%7D%7D%7B%7Bgroovy%7D%7Dprintln%28"Hello%20from"%20%2B%20"%20search%20text%3A"%20%2B%20%2823%20%2B%2019%29%29%7B%7B%2Fgroovy%7D%7D%7B%7B%2Fasync%7D%7D%20". If there is an output, and the title of the RSS feed contains "Hello from search text:42", then the instance is vulnerable. This vulnerability has been patched in XWiki 15.10.11, 16.4.1 and 16.5.0RC1. Users are advised to upgrade. Users unable to upgrade may edit "Main.SolrSearchMacros" in "SolrSearchMacros.xml" on line 955 to match the "rawResponse" macro in "macros.vm#L2824" with a content type of "application/xml", instead of simply outputting the content of the feed.