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[Fwd: Re: Cross-Site Request Forgeries (Re: The Dangers of Allowing Users to Post Images)]
From: Peter W <peterw () usa net>
Date: Sun, 17 Jun 2001 12:22:23 -0400

Regarding IMG tags in HTML email, here is a good point I received off-list.
The sender did not wish to post directly, but approved forwarding this note.

-Peter

----- Forwarded message (anonymous, forwarded with permission) -----

Date: Sat, 16 Jun 2001 22:55:41 +0200
To: Peter W <peterw () usa net>
From: <anonymous>
Subject: Re: Cross-Site Request Forgeries (Re: The Dangers of Allowing Users to Post Images)

On 2001-06-15 at 09:26 -0400, Peter W gifted us with:
              I wonder how it would work in HTML mail clients, though? You
could restrict to the sender's domain, but email is the easiest thing in
the world to spoof. (And an effective attack vector, especially against
things like messageboards that expose email addresses.) HTML email is just
evil evil evil. I can't see much need for HTML email to reference *any*
external documents, or to allow, as Jay Beale suggested, the use of things
like META refresh tags to effect client-pull CSRF attacks.

Personally, I loath HTML email.  However, surely a better approach for
this is simply to restrict IMG links by insisting that the source be
inline to the email.

RFC 2112, multipart/related.  Require that email IMG URLs start "cid:"
in order to be automatically rendered.  Whether or not to _allow_ the
rendering of other IMGs is a more contentious issue.

(Just one of those ideas which I've had floating around for a while,
 mainly to stop tracking of who's reading spam HTML email)

----- End forwarded message -----


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