CVE 2021-39203
WordPress is a free and open-source content management system written in PHP and paired with a MySQL or MariaDB database. In affected versions authenticated users who don't have permission to view private post types/data can bypass restrictions in the block editor under certain conditions. This affected WordPress 5.8 beta during the testing period. It's fixed in the final 5.8 release.
See the
CVE page on Mitre.org
for more details.