MySQL 5.0 before 5.0.92, 5.1 before 5.1.51, and 5.5 before 5.5.6 allows remote authenticated users to cause a denial of service (server crash) via a prepared statement that uses GROUP_CONCAT with the WITH ROLLUP modifier, probably triggering a use-after-free error when a copied object is modified in a way that also affects the original object.