Directory traversal vulnerability in the Slider Revolution (revslider) plugin before 4.2 for WordPress allows remote attackers to read arbitrary files via a .. (dot dot) in the img parameter in a revslider_show_image action to wp-admin/admin-ajax.php.
https://plugins.trac.wordpress.org/browser/patch-for-revolution-slider/trunk/revsliderpatch.php
https://euvd.enisa.europa.eu/vulnerability/EUVD-2014-9540
https://blog.sucuri.net/2014/09/slider-revolution-plugin-critical-vulnerability-being-exploited.html
http://www.exploit-db.com/exploits/34511