The query planner in PostgreSQL before 8.0.11, 8.1 before 8.1.7, and 8.2 before 8.2.2 does not verify that a table is compatible with a "previously made query plan," which allows remote authenticated users to cause a denial of service (server crash) and possibly access database content via an "ALTER COLUMN TYPE" SQL statement, which can be leveraged to read arbitrary memory from the server.