D-Link DNS-343 ShareCenter < 1.05 - Command Injection

### Introduction The purpose of this article is to detail the research that I have recently completed regarding the D-Link DNS 343 ShareCenter. #### 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. ### 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. #### 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. #### 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. ### Credit James Bercegay GulfTech Research and Development ### 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. ### Solution D-Link were notified of these issues June of last year. No update has been released publicly.