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.

MySQL 3.x before 3.23.59, 4.x before 4.0.19, 4.1.x before 4.1.2, and 5.x before 5.0.1, checks the CREATE/INSERT rights of the original table instead of the target table in an ALTER TABLE RENAME operation, which could allow attackers to conduct unauth