From 77ddd5d44f2bf4155d0c9b6f7d05f01713b32d5d Mon Sep 17 00:00:00 2001
From: Jan Kundrát <jkt@kde.org>
Date: Thu, 25 Jun 2020 11:30:51 +0200
Subject: [PATCH] SMTP: Do not ignore TLS errors

This fixes a CVE-2020-15047 (category: CWE-295). Since commit 0083eea5ed
which added initial, experimental support for SMTP message submission,
we have apparently never implemented proper SSL/TLS error handling, and
the code has ever since just kept silently ignoring any certificate
verification errors.  As a result, Trojita was susceptible to a MITM
attack when sending e-mails. The information leaked include user's
authentication details, including the password, and the content of sent
messages.

Sorry for this :(.

Now, this patch re-enabes proper TLS error handling. It was not possible
to directly re-use our code for TLS key pinning which we are using for
IMAP connections. In the Qt TLS code, the decision to accept or not
accept a TLS connection is a blocking one, so the IMAP code relies upon
the protocol state machine (i.e., another layer) for deciding whether to
use or not to use the just-established TLS connection. Implementing an
equivalent code in the SMTP library would be nice, but this hot-fix has
a priority. As a result, SMTP connections to hosts with, e.g.,
self-signed TLS certs, are no longer possible. Let's hope that this is
not a practical problem with Lets Encrypt anymore.

Thanks to Damian Poddebniak for reporting this bug.

Change-Id: Icd6bbb2b0fb3e45159fc9699ebd07ab84262fe37
CVE: CVE-2020-15047
BUG: 423453
---

diff --git a/src/MSA/SMTP.cpp b/src/MSA/SMTP.cpp
index 3a05451..ac1eefc 100644
--- a/src/MSA/SMTP.cpp
+++ b/src/MSA/SMTP.cpp
@@ -21,6 +21,7 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 #include "SMTP.h"
+#include "UiUtils/Formatting.h"
 
 namespace MSA
 {
@@ -32,8 +33,8 @@
     user(user), failed(false), isWaitingForPassword(false), sendingMode(MODE_SMTP_INVALID)
 {
     qwwSmtp = new QwwSmtpClient(this);
-    // FIXME: handle SSL errors properly
-    connect(qwwSmtp, &QwwSmtpClient::sslErrors, qwwSmtp, &QwwSmtpClient::ignoreSslErrors);
+    // FIXME: handle SSL errors in the same way as we handle IMAP TLS errors, with key pinning, etc.
+    connect(qwwSmtp, &QwwSmtpClient::sslErrors, this, &SMTP::handleSslErrors);
     connect(qwwSmtp, &QwwSmtpClient::connected, this, &AbstractMSA::sending);
     connect(qwwSmtp, &QwwSmtpClient::done, this, &SMTP::handleDone);
     connect(qwwSmtp, &QwwSmtpClient::socketError, this, &SMTP::handleError);
@@ -78,6 +79,12 @@
     emit error(msg);
 }
 
+void SMTP::handleSslErrors(const QList<QSslError>& errors)
+{
+    auto msg = UiUtils::Formatting::sslErrorsToHtml(errors);
+    emit error(tr("<p>Cannot send message due to an SSL/TLS error</p>\n%1").arg(msg));
+}
+
 void SMTP::setPassword(const QString &password)
 {
     pass = password;
diff --git a/src/MSA/SMTP.h b/src/MSA/SMTP.h
index 453407d..913bb87 100644
--- a/src/MSA/SMTP.h
+++ b/src/MSA/SMTP.h
@@ -43,6 +43,7 @@
     virtual void setPassword(const QString &password);
     void handleDone(bool ok);
     void handleError(QAbstractSocket::SocketError err, const QString &msg);
+    void handleSslErrors(const QList<QSslError>& errors);
 private:
     QwwSmtpClient *qwwSmtp;
     QString host;