XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Any user with view rights on `XWiki.AttachmentSelector` can execute arbitrary Groovy, Python or Velocity code in XWiki leading to full access to the XWiki installation. The root cause is improper escaping in the "Cancel and return to page" button. This page is installed by default. This vulnerability has been patched in XWiki 15.0-rc-1, 14.10.1, 14.4.8, and 13.10.11. There are no known workarounds for this vulnerability.