SOP Bypass and CSRF via Macro

A co-worker and I have been working diligently on a CSRF exploit via a macro written in VBA. The site we have been working on allows users to send excel files back and forth. My co-worker found there is this nice little VB object called InternetExplorer.Application that basically allows you to invoke an instance of IE through a macro. The "InternetExplorer" ActiveX control gives the attacker full access to not only the persisted cookies, but also the session/temporary cookies that exist in all currently open instances of IE. Note that the "same origin policy" *does not* apply. We can grab the DOM (including persisted and session cookies) of any site/origin.

One example we did to prove this was login at a site with remember-me disabled. We ran the script which then showed all of my cookies at various domains, including the previously mentioned site which only had session cookies. Note the InternetExplorer ActiveX control respects the HttpOnly flag.

Our Proof of Concept macro will recursively iterate through all your IE Favorites and request the current available cookies to each one. If you happen to be currently logged in to that site via IE an authenticated cookie will be displayed in a popup box. We all know what this means. This means once we create this new IE.App object we can now utilize any authenticated sessions a user may have open and send requests on behalf of the user. This IE.App object does not behave like the IE browser does. If you open two instances of your IE browser it will not share session cookies between them because of Same Origin Policy (SOP) restrictions. In the case of invoking the IE.App object it bypasses any SOP security settings. The code is pretty straight forward and is simplified below:

{pseudocode}

Dim ie As InternetExplorer

Set ie = New InternetExplorer

Files = iterate(Favorites dir)

Foreach file

url = readFile(file)

ie.Navigate = url

Do Until ie.ReadyState = READYSTATE_COMPLETE Loop

' Now we get the cookie

MsgBox ie.Document.Cookie

{/pseudocode}

Obviously the code in is a much better PoC (bigger, faster, stronger), but the above is a quick synopsis. In order to have this code run, the victim must either be tricked into opening a malicious Excel/PP/Word document or have really low browser security setttings and visit a site that has VBScript which tries to instantiatethe object within the browser (this is THE WORST situation, but also pretty unlikely).

The general risk of this issue seems pretty low although it is definitely a way around any form of CSRF protection since we could potentially parse the DOM and send any CSRFToken with the request.

We understand a macro is basically unmanaged VBscript code and can do anything on the user’s system for which they are authorized, but the fact the InternetExplorer ActiveX control allows for seeing all current session cookies is a bit scary.

We thought about disclosing this to Microsoft and may still do so, but since it is unmanaged code they will probably turn their heads. If anyone has any thoughts I would love to hear them.