More information about this security flaw is available in the following bug: https://bugzilla.redhat.com/show_bug.cgi?id=2302268 Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
This issue affect 'rubygem-rexml' subpackage, provided by 'ruby' package. That is where the fix should be applied.