[UNIX] Topic Calendar Cross Site Scripting

From: SecuriTeam (support_at_securiteam.com)
Date: 03/24/05

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Date: 24 Mar 2005 19:39:02 +0200

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      Topic Calendar Cross Site Scripting
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.phpbb.com/phpBB/viewtopic.php?t=150857> Topic Calendar is "a
    quite widespread MOD for phpBB all version that will add a calendar to the
    board, using topics as event. The authorizations are managed at forums,
    groups and users level, as the standard phpBB authorizations".

    Due to poor sanitization of the 'start' parameter of Topic Calendar's
    calendar_scheduler.php script a remote attacker can insert arbitrary HTML
    and/or JavaScript into the response returned by the server.

    DETAILS

    Vulnerable Systems:
     * Topic Calendar version 1.0.1

    Vulnerable code:
    Let's look at code from calendar_scheduler.php at line 82:
       <?
       ...
       if ( isset($HTTP_POST_VARS['start']) || isset($HTTP_GET_VARS['start'])
    )
       {
         $start = isset($HTTP_POST_VARS['start']) ? $HTTP_POST_VARS['start'] :
    $HTTP_GET_VARS['start'];
       }
       ...
       ?>

    and at line 375:

       <?
       ...
       $s_hidden_fields .= '<input type="hidden" name="start" value="' .
    $start. '" />';
       ...
       ?>

    As can be seen the $start variable is controlled by a remote user, and as
    can be seen there isn't any control of the value that is inserted into the
    return HTML. Therefore, anyone can inject some HTML code like:
       "><script>alert(document.cookie)</script>

    That will incorporate into:
       <input type="hidden"
    name="start"value=""><script>alert(document.cookie)</script>" />

    Exploit:
    The following URL can be used to test the vulnerability:
    http://www.example.com/phpbb/calendar_scheduler.php?start=%22%3E%3Cscript%3Ealert(document.cookie)%3C/script%3E

    Unofficial patch:
    To fix the XSS bug we can use the function intval() at line 85 of
    calendar_scheduler.php:
       <?
       ...
       if ( isset($HTTP_POST_VARS['start']) || isset($HTTP_GET_VARS['start'])
    )
       {
         $start = isset($HTTP_POST_VARS['start']) ? $HTTP_POST_VARS['start'] :
    $HTTP_GET_VARS['start'];
         $start = intval($start)
       }
       ...
       ?>

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:trivero@jumpy.it> Alberto
    Trivero.

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