This update for enigmail to version 2.0.4 fixes multiple issues.
Security issues fixed:
CVE-2017-17688: CFB gadget attacks allowed to exfiltrate plaintext out of encrypted emails.
enigmail now fails on GnuPG integrity check warnings for old Algorithms (bsc#1093151)
CVE-2017-17689: CBC gadget attacks allows to exfiltrate plaintext out of encrypted emails (bsc#1093152)
This update also includes new and updated functionality:
The Encryption and Signing buttons now work for both OpenPGP and S/MIME.
Enigmail will chose between S/MIME or OpenPGP depending on whether the keys
for all recipients are available for the respective standard
Support for the Autocrypt standard, which is now enabled by default
Support for Pretty Easy Privacy (p≡p)
Support for Web Key Directory (WKD)
The message subject can now be encrypted and replaced with a dummy subject,
following the Memory Hole standard forprotected Email Headers
keys on keyring are automatically refreshed from keyservers at irregular intervals
Subsequent updates of Enigmail no longer require a restart of Thunderbird
Keys are internally addressed using the fingerprint instead of the key ID