Oracle MySQL 5.1.67 and earlier and 5.5.29 and earlier, and MariaDB 5.5.28a and possibly other versions, allows remote authenticated users to cause a denial of service (mysqld crash) via a SELECT command with an UpdateXML command containing XML with a large number of unique, nested elements.
http://rhn.redhat.com/errata/RHSA-2013-0772.html
https://bugzilla.redhat.com/show_bug.cgi?id=882607
http://seclists.org/fulldisclosure/2012/Dec/7
http://secunia.com/advisories/53372
http://security.gentoo.org/glsa/glsa-201308-06.xml
http://www.mandriva.com/security/advisories?name=MDVSA-2013:150
http://www.openwall.com/lists/oss-security/2012/12/02/3
http://www.openwall.com/lists/oss-security/2012/12/02/4
http://www.oracle.com/technetwork/topics/security/cpuapr2013-1899555.html