yum-rhn-plugin in Red Hat Enterprise Linux (RHEL) 5 does not verify the SSL certificate for a file download from a Red Hat Network (RHN) server, which makes it easier for remote man-in-the-middle attackers to cause a denial of service (loss of updates) or force the download and installation of official Red Hat packages that were not requested.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10864
https://bugzilla.redhat.com/show_bug.cgi?id=457113
http://www.securityfocus.com/bid/30695
http://www.redhat.com/support/errata/RHSA-2008-0815.html