Re: [websec] handling STS header field extendability

Paul Hoffman <paul.hoffman@vpnc.org> Mon, 13 August 2012 21:17 UTC

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From: Paul Hoffman <paul.hoffman@vpnc.org>
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To: Collin Jackson <collin.jackson@sv.cmu.edu>
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Cc: Ben Campbell <ben@nostrum.com>, IETF WebSec WG <websec@ietf.org>
Subject: Re: [websec] handling STS header field extendability
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On Aug 13, 2012, at 2:09 PM, Collin Jackson wrote:

> Brad was describing a network attacker that was able to obtain a DV
> certificate (but not an EV certificate) for a target site. The
> attacker can "act as a partial MITM and provide, using a DV
> certificate, trojan script content in an iframe with no security
> indicators or substitute an external script in a legitimate page and
> that script will have full access to content delivered with an EV
> certificate." This would allow, for example, the attacker to read
> cookies and passwords entered into a bank's login form.
> 
> My point is that if the site is using LockEV, the network attacker's
> DV certificate is useless, so LockEV is useful even if the browser's
> script access checks don't pay attention to the EV/DV distinction.

If the site did LockEV without ever locking its public key or CA, you would be right. That seems like a ridiculous policy, though. LockCA seems much more likely.

--Paul Hoffman