1 files changed, 35 insertions, 19 deletions
diff --git a/mailnews/imap/src/nsImapProtocol.cpp b/mailnews/imap/src/nsImapProtocol.cpp
index 940d87cbd..97e61a40e 100644
--- a/mailnews/imap/src/nsImapProtocol.cpp
+++ b/mailnews/imap/src/nsImapProtocol.cpp
@@ -1526,28 +1526,44 @@ void nsImapProtocol::EstablishServerConnection()
   }
   else if (!PL_strncasecmp(serverResponse, ESC_PREAUTH, ESC_PREAUTH_LEN))
   {
-    // we've been pre-authenticated.
-    // we can skip the whole password step, right into the
-    // kAuthenticated state
-    GetServerStateParser().PreauthSetAuthenticatedState();
+    // PREAUTH greeting received. We've been pre-authenticated by the server.
+    // We can skip sending a password and transition right into the
+    // kAuthenticated state; but we won't if the user has configured STARTTLS.
+    // (STARTTLS can only occur with the server in non-authenticated state.)
+    if (!(m_socketType == nsMsgSocketType::alwaysSTARTTLS ||
+          m_socketType == nsMsgSocketType::trySTARTTLS)) {
+      GetServerStateParser().PreauthSetAuthenticatedState();
 
-    if (GetServerStateParser().GetCapabilityFlag() == kCapabilityUndefined)
-      Capability();
+      if (GetServerStateParser().GetCapabilityFlag() == kCapabilityUndefined)
+        Capability();
 
-    if ( !(GetServerStateParser().GetCapabilityFlag() &
-          (kIMAP4Capability | kIMAP4rev1Capability | kIMAP4other) ) )
-    {
-      // AlertUserEvent_UsingId(MK_MSG_IMAP_SERVER_NOT_IMAP4);
-      SetConnectionStatus(NS_ERROR_FAILURE);        // stop netlib
-    }
-    else
-    {
-      // let's record the user as authenticated.
-      m_imapServerSink->SetUserAuthenticated(true);
+      if (!(GetServerStateParser().GetCapabilityFlag() &
+            (kIMAP4Capability | kIMAP4rev1Capability | kIMAP4other))) {
+        // AlertUserEventUsingId(MK_MSG_IMAP_SERVER_NOT_IMAP4);
+        SetConnectionStatus(NS_ERROR_FAILURE);  // stop netlib
+      } else {
+        // let's record the user as authenticated.
+        m_imapServerSink->SetUserAuthenticated(true);
 
-      ProcessAfterAuthenticated();
-      // the connection was a success
-      SetConnectionStatus(NS_OK);
+        ProcessAfterAuthenticated();
+        // the connection was a success
+        SetConnectionStatus(NS_OK);
+      }
+    } else {
+      // STARTTLS is configured so don't transition to authenticated state. Just
+      // alert the user, log the error and drop the connection. This may
+      // indicate a man-in-the middle attack if the user is not expecting
+      // PREAUTH. The user must change the connection security setting to other
+      // than STARTTLS to allow PREAUTH to be accepted on subsequent IMAP
+      // connections.
+      AlertUserEventUsingName("imapServerDisconnected");
+      const nsCString &hostName = GetImapHostName();
+      MOZ_LOG(
+          IMAP, LogLevel::Error,
+          ("PREAUTH received from IMAP server %s because STARTTLS selected. "
+           "Connection dropped",
+           hostName.get()));
+      SetConnectionStatus(NS_ERROR_FAILURE);        // stop netlib
      }
   }