Fix IP address exposure in FTP code

* src/ftp.c (getftp): Do not use PORT when PASV fails.
* tests/FTPServer.px: Add pasv_not_supported server flag.
* tests/Makefile.am: Add Test-ftp-pasv-not-supported.px
* tests/Test-ftp-pasv-not-supported.px: New test

Fix IP address exposure when automatically falling back from
passive mode to active mode (using the PORT command). A behavior that
may be used to expose a client's privacy even when using a proxy.

NEWS

@@ -9,6 +9,8 @@ Please send GNU Wget bug reports to <bug-wget@gnu.org>.
 
 * Changes in Wget X.Y.Z
 
+** Remove FTP passive to active fallback due to privacy concerns
+
 ** Add support for --if-modified-since
 
 ** Add support for metalink through --input-metalink and --metalink-over-http

src/ftp.c

@@ -252,7 +252,6 @@ getftp (struct url *u, wgint passed_expected_bytes, wgint *qtyread,
   char *respline, *tms;
   const char *user, *passwd, *tmrate;
   int cmd = con->cmd;
-  bool pasv_mode_open = false;
   wgint expected_bytes = 0;
   bool got_expected_bytes = false;
   bool rest_failed = false;
@@ -883,13 +882,19 @@ Error in server response, closing control connection.\n"));
                           ? CONERROR : CONIMPOSSIBLE);
                 }
 
-              pasv_mode_open = true;  /* Flag to avoid accept port */
               if (!opt.server_response)
                 logputs (LOG_VERBOSE, _("done.    "));
-            } /* err==FTP_OK */
+            }
-        }
+          else
+            return err;
 
-      if (!pasv_mode_open)   /* Try to use a port command if PASV failed */
+          /*
+           * We do not want to fall back from PASSIVE mode to ACTIVE mode !
+           * The reason is the PORT command exposes the client's real IP address
+           * to the server. Bad for someone who relies on privacy via a ftp proxy.
+           */
+        }
+      else
         {
           err = ftp_do_port (csock, &local_sock);
           /* FTPRERR, WRITEFAILED, bindport (FTPSYSERR), HOSTERR,
@@ -1148,8 +1153,8 @@ Error in server response, closing control connection.\n"));
     }
 
   /* If no transmission was required, then everything is OK.  */
-  if (!pasv_mode_open)  /* we are not using pasive mode so we need
+  if (!opt.ftp_pasv)  /* we are not using passive mode so we need
-                              to accept */
+                         to accept */
     {
       /* Wait for the server to connect to the address we're waiting
          at.  */

tests/FTPServer.pm

@@ -740,6 +740,14 @@ sub run
                     last;
                 }
 
+                if (defined($self->{_server_behavior}{pasv_not_supported})
+                    && $cmd eq 'PASV')
+                {
+                    print {$conn->{socket}}
+                      "500 PASV not supported.\r\n";
+                    next;
+                }
+
                 # Run the command.
                 &{$command_table->{$cmd}}($conn, $cmd, $rest);
             }

tests/Makefile.am

@@ -127,7 +127,8 @@ PX_TESTS = \
              Test--start-pos.px \
              Test--start-pos--continue.px \
              Test--httpsonly-r.px \
-             Test-204.px
+             Test-204.px \
+             Test-ftp-pasv-not-supported.px
 
 EXTRA_DIST = FTPServer.pm FTPTest.pm HTTPServer.pm HTTPTest.pm \
              WgetTests.pm WgetFeature.pm WgetFeature.cfg $(PX_TESTS) \

tests/Test-ftp-pasv-not-supported.px

@@ -0,0 +1,60 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+use FTPTest;
+
+# This test checks whether Wget *does not* fall back from passive mode to
+# active mode using a PORT command. Wget <= 1.16.3 made a fallback exposing
+# the client's real IP address to the remote FTP server.
+#
+# This behavior circumvents expected privacy when using a proxy / proxy network (e.g. Tor).
+#
+# Wget >= 1.16.4 does it right. This test checks it.
+
+###############################################################################
+
+# From bug report 10.08.2015 from tomtidaly@sigaint.org
+my $afile = <<EOF;
+FTP PORT command code in v1.16.3?
+
+In the past it could be possible for a site over http connection to
+redirect wget to FPT using FTP PORT command so the site gets the real IP
+of the computer even when wget proxy command is in use I believe:
+https://lists.torproject.org/pipermail/tor-talk/2012-April/024040.html
+
+Is that code still present in wget v1.16.3? It was present in v1.13.4.
+EOF
+
+$afile =~ s/\n/\r\n/g;
+
+
+# code, msg, headers, content
+my %urls = (
+    '/afile.txt' => {
+        content => $afile,
+    },
+);
+
+my $cmdline = $WgetTest::WGETPATH . " -S ftp://localhost:{{port}}/afile.txt";
+
+my $expected_error_code = 8;
+
+my %expected_downloaded_files = (
+    'afile.txt' => {
+        content => $afile,
+    },
+);
+
+###############################################################################
+
+my $the_test = FTPTest->new (
+                             server_behavior => {pasv_not_supported => 1},
+                             input => \%urls,
+                             cmdline => $cmdline,
+                             errcode => $expected_error_code,
+                             output => \%expected_downloaded_files);
+exit !$the_test->run();
+
+# vim: et ts=4 sw=4