User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:72.0) Gecko/20100101 Firefox/72.0

Steps to reproduce:

Send a signed message to yourself (S/MIME, X.509). Forward this message as attachment to yourself and sign the forwarded message again (S/MIME, X.509).
As an alternative, attach any signed message (S/MIME, X.509) to a signed message.

Actual results:

The forwarded message shows the attached message headers, but not the mail content. The message source shows the content of the attached mail. This bug does not occur when the forwarded message is not signed.

I let display attachements inline. I am on Windows 10, Thunderbird is of version 68.4.2 (32 Bit). I also have Engimail, but it is actually not used here.

Expected results:

The attached mail message should be displayed inline with headers and content.

This is a sample message that does not display message content of attached message.

I can report the same issue, running Thunderbird 68.5.0 (from Debian buster).
Attaching a signed email to a signed email shows up correctly in the composing window (i.e. attachment size is as expected (e.g. 21.5 KB), double-clicking the attachment opens up a new window showing the full content), but after sending it, the mail shows up in the "Sent" folder with the broken attachment (i.e. size 2.0 KB, no body shown).

mutt shows the MIME tree as follows:

I 1 <no description> [multipa/mixed, 7bit, 21K]
I 2 ├─><no description> [text/plain, quoted, utf-8, 0.2K]
A 3 └─>test [message/rfc822, 7bit, 21K]
I 4 └─><no description> [multipa/signed, 7bit, 19K]
I 5 ├─><no description> [multipa/alternativ, 7bit, 13K]
I 6 │ ├─><no description> [text/plain, quoted, iso-8859-1, 1.8K]
I 7 │ └─><no description> [text/html, quoted, iso-8859-1, 11K]
A 8 └─>smime.p7s [applica/pkcs7-sign, base64, 5.7K]
A 9 S/MIME Cryptographic Signature [applica/pkcs7-sign, base64, 4.3K]

and here's the (obfuscated, sorry) raw text:

To: Martin Schuster <Martin.Schuster1@infineon.com>
From: Martin Schuster <martin.schuster1@infineon.com>
Subject: Fwd: test
MIME-Version: 1.0
Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="------------ms070605070205030106090203"

This is a cryptographically signed message in MIME format.

--------------ms070605070205030106090203
Content-Type: multipart/mixed;
boundary="------------0C1E0EF3B01F10E13A5670C0"
Content-Language: en-US

This is a multi-part message in MIME format.
--------------0C1E0EF3B01F10E13A5670C0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: quoted-printable

[...]
--------------0C1E0EF3B01F10E13A5670C0
Content-Type: message/rfc822;
name="tst.eml"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename="tst.eml"

MIME-Version: 1.0
Subject: test
Content-Type: multipart/signed; protocol="application/x-pkcs7-signature";
micalg=SHA1; boundary="----=_NextPart_000_00D9_01D5ECC5.D7FEA540"

------=_NextPart_000_00D9_01D5ECC5.D7FEA540
Content-Type: multipart/alternative;
boundary="----=_NextPart_001_00DA_01D5ECC5.D7FEA540"

------=_NextPart_001_00DA_01D5ECC5.D7FEA540
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

[...]

------=_NextPart_001_00DA_01D5ECC5.D7FEA540
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

[...]
------=_NextPart_001_00DA_01D5ECC5.D7FEA540--

------=_NextPart_000_00D9_01D5ECC5.D7FEA540
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"

M[...]
[...]AAAAAAAA

------=_NextPart_000_00D9_01D5ECC5.D7FEA540--

--------------0C1E0EF3B01F10E13A5670C0--

--------------ms070605070205030106090203
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature

M[...]
[...]AAAAAAAA=
--------------ms070605070205030106090203--

This seems to be related to or a duplicate of Bug 1598584

Indeed Bug 1598584 seems to be the same. I actually did not see it.
Nevertheless, the problem is very annoying and severe in every day work. I would appreciate if someone could at least confirm that the problem persists.

Reporter, do you see this when using version 78?

Yes, I have seen the same problem in all the Thunderbird versions since my reporting, even in 78.4.3 that I am currently using.

Thanks for the update - let's continue in bug 1598584

Or maybe not bug 1598584? AIUI, The reporter there indicates the issue no longer exists.

This is updated version of a message showing the buggy behaviour.

I just updated a sample message showing the bug. Please click the message, open it with Thunderbird. If you cannot read the content of the attachment then you experience the buggy behaviour.
I would be very happy, if this bug could be fixed.
I am not sure whether this relates to bug 1598584. This one concerns S/MIME not Enigmail. Thunderbird does not crash but does not display attachment content.

Using 95.0b3 with Franz's testcase I see only the headers of the attachment.

I am pretty depressed as this bug is still unconfirmed after 2.5 years. The bug is a pain for all people using signatures. As so few people do, there is obviously no urgency to fix it.
It would be nice, if someone could at least confirm that there is a bug.
Currently I use Thunderbird 91.9.0. Attachments are configured to be displayed inline as far as possible. The mail that I uploaded in this thread does show the headers of the attached mails but not its content. Outlook can display the content. Thunderbird cannot. As said, inline Thunderbird just shows the headers. If I click on the attachment it displays an empty canvas, whereas CTRL-U shows the complete attached mail.
The bug occurs only when the mail is signed and the attached mail is signed, too.
If you check and do not see the content of the attached mail, you experience the bug. There has to be a green line in the mail content.
I hope someone listens and proceeds.
Thanks
Franz

Hi folks,
just to remind you that this bug is still a pain and not yet solved. In case you want to know how it has to look like, I uploaded a screenshot of the same message in eM Client.

Ciao
Franz