Encryption failures fixed in popular PGP email security tool Enigmail

Developers of the popular Enigmail email security extension for Thunderbird have fixed several issues that could have exposed messages users believed to be encrypted.

Enigmail provides a graphical user interface in the Mozilla Thunderbird and SeaMonkey programs that allows users to digitally sign and encrypt email messages using the OpenPGP standard.

The Enigmail Project released version 1.7.2 of the extension on Aug. 29 and briefly noted that the release fixes “several important bugs.” The changelog did not contain additional details about the impact of the fixed issues, but included a link to the project’s external bug tracker.

In addition to several non-security issues, the bug tracker lists a number of addressed bugs that could have serious security implications for users of the older Enigmail 1.7 version. One of them causes emails to be sent in unencrypted form when only BCC (blind carbon copy) recipients are specified.

Another issue causes drafts to be saved in plain text when writing a new email even when the email is marked for encryption automatically. If the IMAP protocol is used, the unencrypted drafts can be synchronized with the email server, exposing potentially sensitive information.

This behavior only happens when the system selects an email for encryption automatically based on an existing per-recipient rule or when the recipient’s public key exists in the local key store. “If the email is manually marked to be encrypted (e.g. by clicking the yellow key symbol on the bottom-right) the drafts are correctly encrypted before being sent to the IMAP server,” the bug entry notes.

Another bug can cause an incorrect encryption or signing status message to be displayed when composing a reply. “This especially happens if the compose window is not opened for the first time,” another entry on the bug tracker notes.

A fourth issue that has been addressed can cause an upgrade from Enigmail 1.6 to 1.7 to break encryption. Email messages won’t be encrypted if the “per recipient” setting is disabled under Key Selection, despite other key selection mechanisms like “by email” and “manual if missing” being enabled.

“When confirmation dialog is enabled you can even see that Enigmail wants to send an email unsigned/unencrypted despite having selected forced encryption,” thecorresponding bug entry says. “Otherwise it is silently sent unencrypted.”

An Enigmail user who reported one of the encryption failures in version 1.7 on the project’s support forum described the situation as “the biggest imaginable catastrophe.”

“I am currently preparing a crypto class for journalists next week to teach them how to use safe email,” the user wrote. “HOW am I going to explain that? A system tells the user in a separate window as well as in a menu line that everything will be encrypted but then it simply FORGOT to ENCRYPT and, ooops, their report will be intercepted and their source will be tortured?”