Internet DRAFT - draft-request-header-originated-with
draft-request-header-originated-with
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.
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This Internet-Draft will expire on June 23, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
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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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