The Popup Builder by OptinMonster WordPress plugin before 2.12.2 does not ensure that the campaign to be loaded via some shortcodes is actually a campaign, allowing any authenticated users such as subscriber to retrieve the content of arbitrary posts, like draft, private or even password protected ones.
https://wpscan.com/vulnerability/28754886-b7b4-44f7-9042-b81c542d3c9c