What the vulnerability does
01Description
XWiki is a generic wiki platform. Any user with edit right on a page (could be the user's profile) can execute code (Groovy, Python, Velocity) with programming right by defining a wiki macro. This allows full access to the whole XWiki installation. The main problem is that if a wiki macro parameter allows wiki syntax, its default value is executed with the rights of the author of the document where it is used. This can be exploited by overriding a macro like the children macro that is used in a page that has programming right like the page XWiki.ChildrenMacro and thus allows arbitrary script macros. This vulnerability has been patched in XWiki 16.4.7, 16.10.3 and 17.0.0 by executing wiki parameters with the rights of the wiki macro's author when the parameter's value is the default value.
