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Date: Tue, 15 May 2018 10:22:46 +0200
From: Yves-Alexis Perez <corsac@...ian.org>
To: Brian May <brian@...uxpenguins.xyz>, oss-security@...ts.openwall.com
Subject: Re: PGP/MIME and S/MIME mail clients vulnerabilities

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On Tue, 2018-05-15 at 17:40 +1000, Brian May wrote:
> Have a look at some official statements on this:
> 
> * https://lists.gnupg.org/pipermail/gnupg-users/2018-May/060334.html
> * https://protonmail.com/blog/pgp-vulnerability-efail/
> 
> For the case of PGP it sounds like the only problems occur when mail
> clients ignore the GPG hints.

Thanks for the links (I had already included the information in my summary
though).
> 
> For S/MIME, it does sound like the standard is broken and needs fixing.

That was my understanding as well, thus the mitigations.
> 
> If I understand this correctly, the "Direct Exfiltration" is an attack
> that doesn't require modifying the encrypted data - so presumably the
> MDC in PGP won't help. 

Yes indeed.

> To me this sounds like a email client problem
> (allowing mixing encrypted and encrypted data in the one HTML document
> seems like a very bad idea), but the https://efail.de/ page says the
> standards need to be updated to fix this.

Maybe the fixing the standard will help, but indeed the client can already
sanitize the various chunks of message and not render them as part of one HTML
document. As far as I can tell only Thunderbird was vulnerable to this (in
open-source software), but I can't find a CVE number or a public bug for this.

Regards,
- -- 
Yves-Alexis
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