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TUCoPS :: Web :: PHP :: phpadm.htm

MyPhpAdmin remote command execution



COMMAND

    myPhpAdmin

SYSTEMS AFFECTED

    myPhpAdmin <= 2.2.0rc3

PROBLEM

    Carl Livitt found  following.  Further  to the excellent  research
    done  by  Shaun  Clowes  of  Secure  Reality  Pty  Ltd into remote
    command execution on webservers  running myPhpAdmin, it turns  out
    that there  is another  method of  exploitation.   For details  of
    what phpMyAdmin does, how it works and other security issues  with
    the product, please refer to article SRADV00008:

        http://oliver.efri.hr/~crv/security/bugs/Others/phpadm.html

    The   new   method   involves   an   unchecked   variable  in  the
    'tbl_copy.php'   and   'tbl_rename.php'scripts.    By   passing  a
    carefully crafted URL to these  scripts, it is possible to  insert
    PHP  instructions  into  an  eval()  function thereby enabling the
    attacker to execute arbitrary  commands on the webserver  with the
    privileges of the http daemon, typically 'nobody'.

    The  method  works   perfectly  on  a   default  installation   of
    phpMyAdmin, but has  not been tested  in an environment  where the
    advanced authentication mechanism has been enabled.

    In addition,  this method  assumes that  the 'test'  table in  the
    mySQL  database  has  not  been  removed; in order to successfully
    exploit the vulnerability presented here, it is necessary to  have
    the  ability  to  make  changes  to  tables within a database.  It
    should  be  noted  that  any  database  that phpMyAdmin has access
    rights to is  sufficient: the 'test'  database just happens  to be
    very handy.

    In 'tbl_copy.php' and 'tbl_rename.php' are these lines of code:

          tbl_copy.php: eval("\$message = \"$strCopyTableOK\";");
        tbl_rename.php: eval("\$message =  \"$strRenameTableOK\";");

    These eval() functions are called if  the rest of the code in  the
    script executed successfully.  If  it were possible to modify  the
    contents  of  $strCopyTableOK  or  $strRenameTableOK,  it would be
    possible to execute arbitrary eval() code.

    Fortunately  for  an  attacker,  it  is  possible  to  control the
    contents of either of these variables.  For example, by passing  a
    URL of:

        http://victim/phpmyadmin/tbl_copy.php?strCopyTableOK=".passthru('cat%20/etc/passwd')."

    it  is  possible  to  set  things  up  so  that  the  script dumps
    /etc/passwd.  But  it doesn't.   Why?  Because  earlier code stops
    execution before we get  to the eval():   (Note that the code  has
    been edited for brevity)

        if (isset($new_name) && $new_name!=""){
		        .
	        $result = mysql_query($sql_structure) or mysql_die();
		        .
	        $result = mysql_query($query) or mysql_die();
		        .
	        $result = mysql_query($sql_structure) or mysql_die();
        }
        else mysql_die($strTableEmpty);

    If any of the mysql_query() calls fail, mysql_die() is called  and
    execution stops.  This is no good  to us, as we need the calls  to
    succeed in order  for eval() to  be executed with  our commands in
    it.

    To make sure all the calls  succeed, we need to make sure  that we
    have a database that  we can create tables  in.  This can  be done
    by using 'tbl_create.php' script like so:

        http://victim/phpmyadmin/tbl_create.php?db=test&table=haxor&query=dummy+integer+primary+key+auto_increment&submit=1

    In the default installation, we  don't need to specify a  username
    or  password  and  will  now  have  a  table called 'haxor' in the
    'test' database.  We're now  ready to  exploit the  'tbl_copy.php'
    script:

        http://victim/phpmyadmin/tbl_copy.php?db=test&table=haxor&new_name=test.haxor2&strCopyTableOK=".passthru('cat%20/etc/passwd')."

    Success!  The contents of /etc/passwd are included in the  webpage
    that is returned by this URL.  Of course, the choice of command to
    execute is limited only by the imagination of the attacker.

SOLUTION

    This  is  really  simple  to  fix:  just comment out the offending
    eval()  statements  in  the  'tbl_copy.php'  and  'tbl_rename.php'
    scripts.  The  calls to eval()  are not used  at any point  in the
    script   because   the   $strCopyTableOK   and   $strRenameTableOK
    variables are never  normally defined.   This means it  is safe to
    remove them.

    This isn't so much a problem with phpMyAdmin as it is with PHP  in
    general.  We would  HIGHLY recommend turning off  register_globals
    in  php.ini  (which  is  the  default  in  set in php.ini-dist for
    php4+).  With  that option disabled,  the only thing  that passing
    in extra parameters can do is create entries in the $HTTP_GET_VARS
    array, and it's not possible to clobber global script variables.


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