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                     GulfTech Research and Development                                                                 

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#          D-Link DNS-343 ShareCenter <= 1.05 Command Injection           #
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Released Date: 2017-01-15
Last Modified: 2017-06-22
 Company Info: D-Link
 Version Info: 
              Vulnerable
               D-Link DNS-343 ShareCenter <= 1.05


--[ Table of contents

00 - Introduction
    00.1 Background

01 - Command Injection
    01.1 - Vulnerable code analysis
    01.2 - Remote exploitation

02 - Credit

03 - Proof of concept

04 - Solution

05 - Contact information


--[ 00 - Introduction

The purpose of this article is to detail the research that I have recently 
completed regarding the D-Link DNS 343 ShareCenter.

--[ 00.1 - Background

The D-Link ShareCenter 4-Bay Network Storage Enclosure (DNS-343) connects 
to your network instead of to a computer so everyone on your network can 
back up content to one central location. Plus, it lets you share your 
stored content across your network and over the Internet so family members, 
friends and employees can access it no matter where they are.


--[ 01 - Command Injection

Within the DNS-343 web directory is a folder named "maintenance" that
contains a number of ASP scripts that are related to maintenance tasks that
can be performed. The script by the name of "test_mail.asp" caught my 
attention, and that is what we will focus on for now.

--[ 01.1 - Vulnerable code analysis

The DNS-343 utilizes the goAhead web server, which contains a functionality
called goForms, which basically stores CGI in memory. This is important to
know as the previously mentioned "test_mail.asp" posts directly to the
"/goform/Mail_Test" endpoint. Code for this particular goForm can be found
within the "webs" binary.

int __fastcall sub_27D24(int a1)
{
  int v1; // r4@1
  int *v2; // r10@1
  char *v3; // r8@1
  char *v4; // r6@1
  char *v5; // r5@1
  char *v6; // r7@1
  int v7; // r12@1
  char *v8; // r0@4
  char *v10; // [sp+10h] [bp-230h]@1
  char *v11; // [sp+14h] [bp-22Ch]@1
  char s; // [sp+18h] [bp-228h]@4

  v1 = a1;
  v2 = &dword_8D968;
  v3 = sub_4D340(a1, (int)"f_auth", &byte_7F4B4);
  v11 = sub_4D340(v1, (int)"f_username", &byte_7F4B4);
  v10 = sub_4D340(v1, (int)"f_password", &byte_7F4B4);
  v4 = sub_4D340(v1, (int)"f_smtpserver", &byte_7F4B4);
  v5 = sub_4D340(v1, (int)"f_sender", &byte_7F4B4);
  v6 = sub_4D340(v1, (int)"f_sendto", &byte_7F4B4);
  system("rm /tmp/email_*");
  v7 = (unsigned __int8)*v3 - 49;
  if ( *v3 == 49 )
    v7 = (unsigned __int8)v3[1];
  if ( v7 )
  {
    sprintf(&s, "email -h %s -p 25 -a 0 -s %s -d %s -t", v4, v5, v6);
    v2 = &dword_8D968;
    v8 = &s;
  }
  else
  {
    sprintf(&s, "email -h %s -p 25 -a 1 -u %s -w %s -s %s -d %s -t", v4, 
    v11, v10, v5, v6);
    v8 = &s;
  }
  *v2 = system(v8);
  *v2 = sub_27C80();
  return THISISAREDIRECT(v1, "web/maintenance/test_mail_result.asp");
}

As can be seen in the above psuedo code, the form data passed to the goForm
endpoint is never sanitized, and then used directly in a system call. This
can be leveraged by an unauthenticated remote attacker to execute code as
root and take complete control of the device.

--[ 01.2 - Remote exploitation

Exploiting this issue is trivial, and can be achieved by simply sending a 
post request containing a command injection string within one of the fields
that are affected to the "/goform/Mail_Test" endpoint. I achieved this by 
sending a post request with the following data.

f_smtpserver=;touch /tmp/gulftech;

The above post request successfully creates the file named "gulftech" 
within the /tmp directory as the root user.


--[ 02 - Credit

James Bercegay
GulfTech Research and Development


--[ 03 - Proof of concept

We strive to do our part to contribute to the security community.
Metasploit modules for issues outlined in this paper can be found online.


--[ 04 - Solution

D-Link were notified of these issues June of last year. No update has been
released publicly.


--[ 05 - Contact information

Web
https://gulftech.org/

Mail
security@gulftech.org


Copyright 2018 GulfTech Research and Development. All rights reserved.