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Re: [ietf-dkim] Mailsploit

Steve Atkins <steve@wordtothewise.com> Tue, 05 December 2017 21:39 UTC

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From: Steve Atkins <steve@wordtothewise.com>
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Subject: Re: [ietf-dkim] Mailsploit
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> On Dec 5, 2017, at 1:24 PM, Pawel Lesnikowski <lesnikowski@limilabs.com> wrote:
> 
> Hi All,
> 
> I'm not sure if you noticed but it seems many client are affected by 'mailsploit':
> https://www.mailsploit.com/index
> 
> Basically the attacker uses special characters inside encoded words to spoof the sender:
> 
> From: =?utf-8?b?cG90dXNAd2hpdGVob3VzZS5nb3Y=?==?utf-8?Q?=00?==?utf-8?b?cG90dXNAd2hpdGVob3VzZS5nb3Y=?=@mailsploit.com
> 
> Such header naively decoded incorrectly is:
> potus@whitehouse.gov\0potus@whitehouse.gov@mailsploit.com
> 
> Although it's not a direct attack on DKIM, if DKIM is implemented properly and email address decoding and displaying isn't, users might be fooled.
> 
> Of course encoded words are not allowed inside email addresses (address, not names), 
> but is seems many clients try to decode them.
> 
> What are your thoughts?

It's a DMARC issue rather than a DKIM one.

Most mobile clients and many desktop clients don't display the senders email address anyway, just the "friendly from" / human readable comment, so "From: POTUS potus@whitehouse.gov <bob@mail.ru>" is much simpler and nearly as effective.

This[1] is a rendering bug the MUA authors really should fix, but not a terrible concern unless maybe you're looking at sneaky targeted phishing mail.

Cheers,
  Steve

[1] mailsploit, I mean. Maybe that other thing too.
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