The Timeline Block – Beautiful Timeline Builder for WordPress (Vertical & Horizontal Timelines) plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 1.3.3 via the tlgb_shortcode() function due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with Author-level access and above, to disclose private timeline content via the id attribute supplied to the 'timeline_block' shortcode.