[Enigmail] [ANN] Enigmail 2.0.5 available - full protection against Efail

Patrick Brunschwig patrick at enigmail.net
Mon May 21 18:38:29 CEST 2018

I have released Enigmail v2.0.5 for Thunderbird version 52 and SeaMonkey
2.46 and newer.

This version prevents against all forms of the "Efail" vulnerability
(https://efail.de) and similar attacks. I strongly recommend to upgrade
to Enigmail 2.0.5 as soon as possible.


Efail: protect against any form of the vulnerability
The approaches of the Thunderbird developers and me so far to prevent
against the Efail vulnerability were focused on fixing HTML displaying.
However, that's quite difficult -- the developers are working on this
for a full week now. And we cannot be sure that it will be impossible to
overcome this.

I have now followed a completely different strategy, which changes a
paradigm in the behavior of Enigmail: up to now, whenever Thunderbird
requested Enigmail to decrypt a PGP/MIME message part, Enigmail did what
it was told: decrypt that MIME part. The idea was that that's what the
user expects. But that's true -- there is only a very small number of
message structures that are created by mail clients. Any other message
structures are manually made up, potentially to attack a victim.

I have therefore changed Enigmail to only decrypt PGP/MIME message
parts, if either
(1) the message is entirely encrypted, or
(2) if the MIME part represents an attached email that itself is fully

In any other case, Enigmail would no longer decrypt anything, and thus
disable any Efail attack. Also, the option "Display Attachments Inline"
will no longer work for attached encrypted emails.

There are, however, a few glitches as Thunderbird doesn't always give me
enough details. For example, in the case of (2), pictures embedded in a
HTML message will not be displayed. I will address this issue, but it
requires a Thunderbird API change, and thus will be available earliest
with Thunderbird 67.

Obtaining Enigmail
Enigmail can be downloaded from

The changelog is available from

Additional Remarks
The new version is still waiting for approval on
https://addons.mozilla.org; you should receive it automatically via the
addons-update once the approval is made.


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