Kaltura - Remote Code Execution and Cross-Site Scripting Sep 24 2017 03:06PM
robin verton telekom de
Telekom Security

Advisory: Kaltura - Remote Code Execution and Cross-Site Scripting
Release Date: 2017/09/12
Author: Robin Verton (robin.verton (at) telekom (dot) de [email concealed])
CVE: CVE-2017-14141, CVE-2017-14142, CVE-2017-14143

Application: Kaltura <= 13.1.0
Risk: Critical
Vendor Status: Kaltura 13.2.0 was released to fix this vulnerabilities.


Quote from Wikipedia:
"Kaltura is a New York-based software company founded in 2006. Kaltura states
that its mission is to power any video experience. Kaltura operates in four
major markets for video based solutions: Cloud TV (AKA OTT TV) for operators
and media companies, OVP (Online Video Platform) offered mostly to media
companies and brands looking to distribute content or monetize it, EdVP
(Education Video Platform) offered to educational institutions who are
increasingly relying on video as for teaching and learning, and EVP
(Enterprise Video Platform) offered to enterprises who use video for
collaboration, communications and marketing."

Kaltura is installed on a lot of high profiles website like banking websites,
universities, manufacturers, multimedia corporations etc.

Multiple vulnerabilities were identified in the current release of the
Kaltura Video platform. It was discovered that Kaltura passes unfiltered user
input to unserialize(), leading to the execution of PHP code. One of this
vulnerabilities can also be triggered unauthenticated. Several other
Cross-Site Scripting vulnerabilities were found.


1) Unauthenticated Remote Code Execution through unserialize() from cookie data

Because of a hardcoded cookie secret, the cookie signature validation can
be bypassed and malicious user input can be passed via the 'userzone' cookie
to the unserialize() function:

abstract class kalturaAction extends sfAction
private $cookieSecret = 'y3tAno3therS$cr3T';

// [...]

protected function getUserzoneCookie()
$cookie = $this->getContext()->getRequest()->getCookie('userzone');
$length = strlen($cookie);
if ($length <= 0)
return null;

$serialized_data = substr($cookie, 0, $length - 32);
$hash_signiture = substr($cookie, $length - 32);

// check the signiture
if (md5($serialized_data . $this->cookieSecret) != $hash_signiture)
return null;

$userzone_data = unserialize(base64_decode($serialized_data));

To pass this validation the base64 encoded serialized object has to be
hashed and this hash appended to the encoded data. A Zend Framework POP
chain [1] can then be used to execute PHP code when unserializing. When
using PHP7 a different chain has to be used because the e-modifier for
preg_replace is not available anymore.

To execute the getUserzoneCookie() function the getAllEntriesAction has to
be called with a valid entry ID. This ID can be obtained from any public
video object which is embedded and typically begins with '0_'.

2) Authenticated Remote Code Execution through unserialize() in the admin panel

The admin panel provides a few 'Developer System Helper' functions to
encode/decode user supplied data. The 'wiki_decode' function will take user
input and pass it nearly untouched to unserialize():

// slightly formatted for better readability
if ( $algo == "wiki_encode" )
$res = str_replace(
array ( "|" , "/") , array ("|01" , "|02"),

By passing a base64 encoded malicious serialized object, PHP code can be

3) Multiple Cross-Site Scripting vulnerabilities under the API path

A few cross-site scripting vulnerabilities were found earlier this year and
fixed [2]. However, this fix was insufficient because PHPs strip_tags()
function only strips tags and is not adequate to secure against XSS
vulnerabilities. There are a few places where this can be exploited to
inject javascript code:

// server/admin_console/web/tools/bigRedButton.php, line 8
$partnerId = strip_tags($_GET['partnerId']);

// [...]

var partnerId = <?php echo $partnerId; ?>;

As can be seen above no tags need to be inserted here to execute javascript
code. A simple partnerId=alert(1) will be executed in this scenario. This
also affects a few other files.

- $_GET['partnerId']
- $_GET['playerVersion']

- $_GET['partnerId']
- $_GET['playerVersion']
- $_GET['secret']
- $_GET['entryId']
- $_GET['adminUiConfId']
- $_GET['uiConfId']

- $_GET['streamUsername']
- $_GET['streamPassword']
- $_GET['streamRemoteId']
- $_GET['streamRemoteBackupId']
- $_GET['entryId']

- $_GET['entryId']

- $_GET['partnerId']
- $_GET['playerVersion']

Additional notes:

The already published Server Side Request Forgery attack [3] was not fixed
properly, because only an additional check for the http(s) protocol was added.
This still allows to talk to some backend services (like the memcached) or
other machines. There is a whitelist in place to make this more secure, but I
could not find a way how to set this up. This is likely responsible for a
lot of insecure default installations of Kaltura in the wild.


[1]: https://www.owasp.org/images/9/9e/Utilizing-Code-Reuse-Or-Return-Oriente
[2]: https://github.com/kaltura/server/pull/5304/files
[3]: http://www.security-assessment.com/files/documents/advisory/Kaltura-Mult


It is recommended to upgrade to the latest version of Kaltura.

Disclosure Timeline:

16. August 2017 - Notified vendor
22. August 2017 - Remote Command Execution vulnerabilities fixed
05. September 2017 - Cross-Site scripting vulnerabilities fixed
11. September 2017 - Kaltura 13.2.0 released
12. September 2017 - Released advisory

About Telekom Security:

Telekom Security is the security provider for Deutsche Telekom and Deutsche Telekom customers.


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