The com_rss option (rss.php) in (1) Mambo and (2) Joomla! allows remote attackers to cause a denial of service (disk consumption and possibly web-server outage) via multiple requests with different values of the feed parameter.
https://exchange.xforce.ibmcloud.com/vulnerabilities/26131
http://www.securityfocus.com/archive/1/431317/100/0/threaded
http://irannetjob.com/content/view/209/28/
http://archives.neohapsis.com/archives/bugtraq/2006-04/0380.html