a null pointer dereference in the add_key_field function in sql/sql_select.cc at line 6559

This vulnerability in MariaDB originates from a null pointer dereference in the add_key_field function in sql/sql_select.cc at line 6559. The issue occurs when the possible_keys pointer is not validated before invoking stat[0].keys.merge(possible_keys), potentially leading to a segmentation fault when executing queries involving certain join conditions. This can be exploited to cause a denial-of-service (DoS) via crafted SQL inputs.