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	Thu, 22 Jan 2015 09:25:39 +0200 (EET)
From: Tomi Ollila <tomi.ollila@iki.fi>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>,
	notmuch mailing list <notmuch@notmuchmail.org>
Subject: Re: privacy problem: text/html parts pull in network resources
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Date: Thu, 22 Jan 2015 09:25:39 +0200
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On Wed, Jan 21 2015, Daniel Kahn Gillmor <dkg@fifthhorseman.net> wrote:

> If i send a message with a text/html part (either it's only text/html,
> or all parts are rendered, or it's multipart/alternative with only a
> text/html subpart) and that HTML has <img
> src="http://example.org/test.png"/> in it, then notmuch will make a
> network request for that image.

I noticed the same a few days ago and first test to avoid that was 

(defun open-network-stream (&rest) nil)

(but then I tried to send email and that failed ;/)

next was M-x debug-on-entry RER open-network-stream RET

... but I don,t remember how to manipulate how that continues.

Latest I've been thinking defadvice around open-network-stream which
asks whether to proceed to it or just return nil.

I'd like to have buffer-local defadvices... ;) .. but there one could
probably store original open-network-stream location and then flet (or
was it letf) it there...

Anyway, if there is better, more robust alternative I am (also) very
interested of it...

Tomi


>
> This is a privacy disaster, because it enables an e-mail sender to use
> "web bugs" to tell when a given notmuch user has opened their e-mail.
>
> It's also a bit of a consistency/storage/indexing disaster because it
> means that what you see when you open a given message will change
> depending on the network environment you're in when you open it.
>
> It's also potentially a security problem because it means that anyone in
> control of the remote server (or the network between you and the remote
> server if the image isn't sourced over https) can feed arbitrary data
> into whatever emacs image rendering library is being used.  (granted,
> this is not a unique problem because this can already be done by the
> original message sender with a multipart/mixed message, but it's an
> additional exposure of attack surface)
>
> I just raised this on #notmuch, and i don't have the time or the
> knowledge to look into it now, but i think the defaults here need to be
> to avoid network access entirely unless the user explicitly requests it.
>
>    --dkg
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