seems likely that its the same cause as MDEV-24121

can you include which python interface you are using and its version?

Sample code also welcome.

I use python 3.6 and the mysql-connector 8.0.18 on CentOS7.8
here some sample code:

import mysql.connector as db_connector

db_connection = db_connector.connect(user="root", password=root_pw, unix_socket=socket_path, database="mysql",use_pure=True)

db_cursor = db_connection.cursor(prepared=True)

#Here the error will thrown.

db_cursor.execute("select version()")

Using the the maraidb python connector build with the mariadb C client lib will work, but needs some source modification, because "use_pure" for example is unknown to the mariadb implementation. So an simple replace of "import mysql.connector as db_connector" to "import mariadb as db_connector" does not work in all cases.

This is a bug in mysql-connector-python. I've reported it as https://bugs.mysql.com/bug.php?id=101479

Latest MariaDB releases have stricter packet validation as a security measure and these broken packets are now rejected.
Meanwhile we're currently discussing whether to relax the packet validation to allow these invalid packets as a special exception.

After many workarounds i tried today this the solutions i got

1- upgrade to php 7.3 or 7.4
(many websites will be down after php upgrades )

2- downgrade to minor version ( EX: mariadb 10.4.16 to 10.4.15)

yum downgrade MariaDB-server MariaDB-common MariaDB-shared MariaDB-client MariaDB-compat MariaDB-devel