SEC Consult SA-20140411-0 :: Multiple vulnerabilities in Plex Media Server

SEC Consult Vulnerability Lab Security Advisory < 20140411-0 >
=======================================================================
              title: Multiple vulnerabilities
            product: Plex Media Server
 vulnerable version: confirmed in 0.9.9.10
      fixed version: none
             impact: High
           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. Use of plain text protocols
Plain text protocols are used in various places.

The Plex App Store fetches App listings and App code via HTTP. This enables
active attackers (MITM) to run code in the context of the Plex Media Server.
The Plex "Remote" functionality uses HTTP as well. This enables passive
attackers to gain access to the session token in order to access the Plex Media
Server web interface.


2. Insecure use of SSL/TLS
The Plex Media Server offers HTTPS access via TCP port 32443. The certificate
that is used is issued by "DigiCert Secure Server CA" which is a commonly
trusted certificate authority. The certificate is issued to "*.hub.plex.tv".
The private key for this certificate is included in the Plex software and can
be extracted easily.
The DNS server behind "hub.plex.tv" is configured to resolve subdomains
relative to the IP indicated in the name. Eg. 1-2-3-4.hub.plex.tv resolves
to the IP 1.2.3.4. This enables all Plex Media Servers to offer SSL/TLS
services out of the box without prior configuration and using a valid
certificate.
For this to work the corresponding private key has to be included in the
software. This enables active attackers to execute SSL MITM attacks as the
private key is effectively public.

This mechanism can be abused by malicious entities to provide services on
arbitrary IPs via SSL/TLS as well. One example would be to run a
watering-hole-style attack by abusing the reputation of the Plex domain as
well as the valid certificate.

As this mechanism requires the private key to be compromised it should not be
used in the first place. The certificate should be revoked.

Note:
The Plex Media Server seems to offer DHE ciphers (DHE_RSA). The perfect forward
secrecy (PFS) properties of these KEX ciphers would prevent passive attackers
from decrypting communication.


3. Unauthenticated information disclosure through stack traces
Python stack traces are included in the responses for some requests. This
allows an attacker to gain information about the target operating system,
local file paths etc. which can be used in further attacks.


4. Cross Site Request Forgery
The application does not implement any kind of CSRF protection. Quite the
contrary, security mechanisms that would minimize the extent of CSRF attacks
are deliberately disabled. The Plex Media Server explicitly allows all
sources (wildcard) in cross-server resource sharing (CORS) as well as in
cross-domain policy restrictions (Flash and Silverlight). This enables
attackers to retrieve arbitrary content (eg. the master token) from the
server.


Proof of concept:
-----------------
1. Use of plain text protocols
No proof of concept needed.
The Plex App store is located at: http://nine.plugins.plexapp.com


2. Insecure use of SSL/TLS
The private key for the "*.hub.plex.tv" certificate:

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----


3. Unauthenticated information disclosure through stack traces
The following request causes an exception in the application logic.

GET /system/proxy HTTP/1.1
Host: <HOST>
X-Plex-Url: http://my.plexapp.com/NONEXISTANT

A stack trace is included in the server's response:

HTTP/1.0 500 Internal Server Error
Content-Length: 3437
Content-Type: application/xml
Cache-Control: no-cache
X-Plex-Protocol: 1.0

<?xml version='1.0' encoding='utf-8'?>
<Response code="2000" status="HTTPError: ">
  <Traceback>Traceback (most recent call last):
  File "C:\Users\user\AppData\Local\Plex Media
Server\Plug-ins\Framework.bundle\Contents\Resources\Versions\2\Python\Framework\components\runtime.py",
line 845, in handle_request
    result = f(**d)
[...]
  File "C:\Program Files (x86)\Plex\Plex Media Server\python27.zip\urllib2.py", line 629, in
http_error_302
    return self.parent.open(new, timeout=req.timeout)
  File "C:\Program Files (x86)\Plex\Plex Media Server\python27.zip\urllib2.py", line 410, in open
    response = meth(req, response)
  File "C:\Program Files (x86)\Plex\Plex Media Server\python27.zip\urllib2.py", line 523, in
http_response
    'http', request, response, code, msg, hdrs)
  File "C:\Program Files (x86)\Plex\Plex Media Server\python27.zip\urllib2.py", line 448, in error
    return self._call_chain(*args)
  File "C:\Program Files (x86)\Plex\Plex Media Server\python27.zip\urllib2.py", line 382, in _call_chain
    result = func(*args)
  File "C:\Program Files (x86)\Plex\Plex Media Server\python27.zip\urllib2.py", line 531, in
http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
HTTPError: HTTP Error 404: Not Found
</Traceback>
</Response>


4. Cross Site Request Forgery
No CSRF tokens are implemented.
The files crossdomain.xml and clientaccesspolicy.xml in the webroot allow
both Silverlight and Flash to send arbitrary requests to the server and
receive responses.
Some pages respond with the "Access-Control-Allow-Origin: *" headers.


Vulnerable / tested versions:
-----------------------------
The vulnerabilities have been verified to exist in Plex Media Server version
0.9.9.10.


Vendor contact timeline:
------------------------
2014-02-09: Contacting vendor through elan () plexapp 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.
2014-02-21: Requesting clarification regarding fixed version.
2014-02-21: Vendors provides further information about reported vulnerabilities.
2014-02-24: Requesting clarification regarding patching status and setting
                        deadline (2014-03-24).
2014-02-25: Vendor announces that the certificate will be revoked soon.
2014-04-04: Requesting status update.
2014-04-05: Vendor confirms that certificate has been revoked. No other fixes
                        have been implemented.
2014-04-11: SEC Consult releases security advisory.


Solution:
---------
No solution is available.


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


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


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