Smooth Slider <= 2.8.6 - Authenticated SQL Injection

Description

During the security analysis, ThunderScan discovered SQL injection
vulnerability in Smooth Slider WordPress plugin.

The easiest way to reproduce the vulnerability is to visit the
provided URL while being logged in as administrator or another user
that is authorized to access the plugin settings page. Users that do
not have full administrative privileges could abuse the database
access the vulnerability provides to either escalate their privileges
or obtain and modify database contents they were not supposed to be
able to.

Due to the missing nonce token, the vulnerable code is also directly
exposed to attack vectors such as Cross Site request forgery (CSRF).

3.1. SQL injection
Function: $wpdb->get_var()
Variable: $_GET['trid']
Vulnerable URL: http://vulnerablesite.com/wp-admin/post.php?post=1&action=edit&source_lang=1&trid=22 OR SLEEP(5)
File: smooth-slider\smooth-slider.php
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470 $id = $wpdb->get_var( "SELECT element_id FROM {$wpdb->prefix}icl_translations WHERE trid=".$_GET['trid']." AND language_code='".$_GET['source_lang']."'" );
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