Receiving S/MIME signed e-mails "no visible content"

Infos:

  • Used Zammad version: 3.4.x
  • Used Zammad installation source: (source, package, …): Repository
  • Operating system: Ubuntu 18.04 LTS
  • Browser + version: Firefox 79, Chrome 84

Expected behavior:

  • Ability to read S/MIME signed (not encrypted) e-mails

Actual behavior:

  • e-mail contains “no content visible”

Steps to reproduce the behavior:

  • get an s/mime signed e-mail

Is this intended? Is there a workaround? We want to be able to read s/mime signed e-mails.

Thanks!

Are you really sure that the message is not encrypted?
Did you try t o download the affected message “RAW” and view it inside of e.g. Thunderbird?

Above message usually only appears if the message is encrypted or empty.
Message signage should have nothing to do with that at all.

We had a look into the mail source code. There we see, that the message is just signed:

Content-Type: application/pkcs7-mime; smime-type=signed-data; name=“smime.p7m”
Content-Disposition: attachment; filename=“smime.p7m”
Content-Transfer-Encoding: base64

Nope sorry, impossible to help you.
My guess is that the mail is empty at this moment.

This is how a smime signed mail looks like (right from the first line below the headers).

This is an S/MIME signed message
------DB0A8603FEC143B828778CD72C7611C6
Date: Wed, 19 Aug 2020 16:01:30 +0200
From: Marcel Herrguth via Zammad Helpdesk <mail@example.com>
To: Marcel Herrguth <user@example.net>
Message-ID: <20200819140129.XYZ371386881337@example.com>
In-Reply-To: 
References: 
Subject: MH Verification
Mime-Version: 1.0
Content-Type: multipart/mixed;
 boundary="--==_mimepart_5f3d30ba227d5_72734926d881336e5";
 charset=UTF-8
Content-Transfer-Encoding: 7bit


----==_mimepart_5f3d30ba227d5_72734926d881336e5
Content-Type: multipart/alternative;
 boundary="--==_mimepart_5f3d30ba225cc_72734926d881334b7";
 charset=UTF-8
Content-Transfer-Encoding: 7bit


----==_mimepart_5f3d30ba225cc_72734926d881334b7
Content-Type: text/plain;
 charset=UTF-8
Content-Transfer-Encoding: base64

[...]

The file smime.p7m is simply the ceritificate used for verification. And technically has nothing to do with the content living in the source of a mail. (Apart the signage). If above you provided is everything of the body, Zammad has nothing to display which is why “no visible content” will appear to indicate exactly that.