MainWP Child < 6.1.2 - Unauthenticated Administrator Authentication Bypass via Passwordless Site Registration

The MainWP Child WordPress plugin before 6.1.2 does not verify the requester's identity in its site-registration request handler when password authentication has been disabled for the targeted account, allowing an unauthenticated attacker to obtain a valid authentication session as that account, including an administrator, by naming its login in a single registration request.