MySQL 5.1 before 5.1.51 and 5.5 before 5.5.6 allows remote authenticated users to cause a denial of service (mysqld server crash) by performing a user-variable assignment in a logical expression that is calculated and stored in a temporary table for GROUP BY, then causing the expression value to be used after the table is created, which causes the expression to be re-evaluated instead of accessing its value from the table.
https://exchange.xforce.ibmcloud.com/vulnerabilities/64843
https://bugzilla.redhat.com/show_bug.cgi?id=640819
http://www.vupen.com/english/advisories/2011/0345
http://www.vupen.com/english/advisories/2011/0170
http://www.vupen.com/english/advisories/2011/0105
http://www.ubuntu.com/usn/USN-1397-1
http://www.ubuntu.com/usn/USN-1017-1
http://www.turbolinux.co.jp/security/2011/TLSA-2011-3j.txt
http://www.securityfocus.com/bid/43676
http://www.redhat.com/support/errata/RHSA-2011-0164.html
http://www.redhat.com/support/errata/RHSA-2010-0825.html
http://www.mandriva.com/security/advisories?name=MDVSA-2010:223
http://www.mandriva.com/security/advisories?name=MDVSA-2010:222
http://www.debian.org/security/2011/dsa-2143
http://support.apple.com/kb/HT4723
http://secunia.com/advisories/42936
http://secunia.com/advisories/42875
http://lists.apple.com/archives/security-announce/2011//Jun/msg00000.html
http://dev.mysql.com/doc/refman/5.5/en/news-5-5-6.html