Yes, your read the title correctly: an unprivileged user can crash your MySQL Server. This applies for the default configuration of MySQL 8.0.21 (and it is probably the case for all MySQL 8 GA versions). Depending on your configuration, it might also be the case for MySQL 5.7. This needs malicious intent and a lot of determination, so no need to panic as this will not happen by accident. I am not sharing the exploit in this post (I might do it later), but I am telling you how to avoid the problem.