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Tiki Wiki CMS Groupware <= 8.2 (snarf_ajax.php) Remote PHP Code Injection

Tiki Wiki CMS Groupware <= 8.2 (snarf_ajax.php) Remote PHP Code Injection

author...........: Egidio Romano aka EgiX
mail.............: n0b0d13s[at]gmail[dot]com
software link....: http://info.tiki.org/

[-] Vulnerability explanation:

The vulnerable code is located into /lib/wiki-plugins/wikiplugin_snarf.php:

170.   // If the user specified a more specialized regex
171.   if ( isset($params['regex']) && isset($params['regexres']) && preg_match('/^(.)(.)+\1[^e]*$/', $params['regex']) ) {
172.      $snarf = preg_replace( $params['regex'], $params['regexres'], $snarf );
173.   }

input passed through $_REQUEST['regex'] is checked by a regular expression at line 171 to prevent
execution of arbitrary PHP code using the  'e'  modifier in a call to preg_replace() at line 172.
But  this  check  could  be  bypassed  with a  null byte injection,  requesting an URL like this:


Tiki internal filters remove  all null bytes  from user input,  but for some strange reason  this
doesn't  happen within admin sessions. So, successful exploitation of this vulnerability requires
an user account with  administration  rights and  'PluginSnarf'  to be enabled  (not by default).

[-] Disclosure timeline:

[23/11/2011] - Vulnerability discovered
[24/11/2011] - Issue reported to security(at)tikiwiki.org
[24/11/2011] - New ticket opened: http://dev.tiki.org/item4059
[27/11/2011] - Vendor confirmed the issue
[27/11/2011] - CVE number requested
[28/11/2011] - Assigned CVE-2011-4558
[22/12/2011] - After four weeks still no fix released
[23/12/2011] - Public disclosure