MainWP Child <= 5.3.3 - Missing Authorization to Unauthenticated Privilege Escalation

The MainWP Child – Securely Connects to the MainWP Dashboard to Manage Multiple Sites plugin for WordPress is vulnerable to privilege escalation due to a missing authorization checks on the register_site function in all versions up to, and including, 5.2 when a site is left in an unconfigured state. This makes it possible for unauthenticated attackers to log in as an administrator on instances where MainWP Child is not yet connected to the MainWP Dashboard. IMPORTANT: this only affects sites who have MainWP Child installed and have not yet connected to the MainWP Dashboard, and do not have the unique security ID feature enabled. Sites already connected to the MainWP Dashboard plugin and do not have the unique security ID feature enabled, are NOT affected and not required to upgrade. Please note versions up to 5.3.3 contained a patch, though a bypass was discovered and not addressed until version 5.3.4.