MySQL 4.x before 4.0.21, and 3.x before 3.23.49, allows attackers to cause a denial of service (crash or hang) via multiple threads that simultaneously alter MERGE table UNIONs.
https://exchange.xforce.ibmcloud.com/vulnerabilities/17667
http://www.securityfocus.com/bid/11357
http://www.redhat.com/support/errata/RHSA-2004-611.html
http://www.gentoo.org/security/en/glsa/glsa-200410-22.xml
http://www.debian.org/security/2004/dsa-562
http://securitytracker.com/id?1011606