XWiki Platform: Privilege escalation (PR) from user registration through PDFClass

XWiki Platform is a generic wiki platform. Starting in version 3.0.1 and prior to versions 4.10.20, 15.5.4, and 15.10-rc-1, remote code execution is possible via PDF export templates. This vulnerability has been patched in XWiki 14.10.20, 15.5.4 and 15.10-rc-1. If PDF templates are not typically used on the instance, an administrator can create the document `XWiki.PDFClass` and block its edition, after making sure that it does not contain a `style` attribute. Otherwise, there are no known workarounds aside from upgrading.