CVE 2021-39200

WordPress is a free and open-source content management system written in PHP and paired with a MySQL or MariaDB database. In affected versions output data of the function wp_die() can be leaked under certain conditions, which can include data like nonces. It can then be used to perform actions on your behalf. This has been patched in WordPress 5.8.1, along with any older affected versions via minor releases. It's strongly recommended that you keep auto-updates enabled to receive the fix.

See the CVE page on Mitre.org for more details.