plugins/system/remember/remember.php in Joomla! 2.5.x before 2.5.10 and 3.0.x before 3.0.4 does not properly handle an object obtained by unserializing a cookie, which allows remote authenticated users to conduct PHP object injection attacks and cause a denial of service via unspecified vectors.
http://www.exploit-db.com/exploits/25087
http://developer.joomla.org/security/85-20130406-core-dos-vulnerability.html
http://archives.neohapsis.com/archives/bugtraq/2013-04/0232.html