D-Link DNS-343 ShareCenter 1.05 Command Injection

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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  
[email protected]  
  
  
Copyright 2018 GulfTech Research and Development. All rights reserved.  
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