The XML_RPC_cd function in lib/pear/XML/RPC.php in Revive Adserver before 3.0.6 allows remote attackers to cause a denial of service (CPU and memory consumption) via a crafted XML-RPC request, aka an XML Entity Expansion (XEE) attack.
http://www.securityfocus.com/bid/71721
http://www.securityfocus.com/archive/1/534264/100/0/threaded