[ 2021-10-02 ][BUUCTF] 集训第五天

2023-12-27 12:43:57

[MRCTF2020]PYWebsite

查看源码

    function enc(code){
      hash = hex_md5(code);
      return hash;
    }
    function validate(){
      var code = document.getElementById("vcode").value;
      if (code != ""){
        if(hex_md5(code) == "0cd4da0223c0b280829dc3ea458d655c"){
          alert("您通过了验证！");
          window.location = "./flag.php"
        }else{
          alert("你的授权码不正确！");
        }
      }else{
        alert("请输入授权码");
      }
    }

输入的validate code的md5值要==0cd4da0223c0b280829dc3ea458d655c
解密你就输了
看看/flag.php

你可是黑阔鸭 IP呀伪造呀

[0CTF 2016]piapiapia

源码泄露
dirsearch扫描不出，dirmap可以
代码审计
弱项

先审计index.php

<?php
	require_once('class.php');
	if($_SESSION['username']) {
		header('Location: profile.php');
		exit;
	}
	if($_POST['username'] && $_POST['password']) {
		$username = $_POST['username'];
		$password = $_POST['password'];

		if(strlen($username) < 3 or strlen($username) > 16) 
			die('Invalid user name');

		if(strlen($password) < 3 or strlen($password) > 16) 
			die('Invalid password');

		if($user->login($username, $password)) {
			$_SESSION['username'] = $username;
			header('Location: profile.php');
			exit;	
		}
		else {
			die('Invalid user name or password');
		}
	}
	else {
?>

用户名和密码长度不得超过3，怪不得sql注入一直invalid
观察到session和重定向profile.php，初步判断可能是session反序列化

审计profile.php

<?php
	require_once('class.php');
	if($_SESSION['username'] == null) {
		die('Login First');	
	}
	$username = $_SESSION['username'];
	$profile=$user->show_profile($username);
	if($profile  == null) {
		header('Location: update.php');
	}
	else {
		$profile = unserialize($profile);
		$phone = $profile['phone'];
		$email = $profile['email'];
		$nickname = $profile['nickname'];
		$photo = base64_encode(file_get_contents($profile['photo']));
?>

观察到很重要的函数unserialize，
其实当时拿到源码判断session反序列化的时候就应该全局搜索unserialize

观察到file_get_contents()，反序列化结束和利用的标志，如果我们把$profile[‘photo’]替换为config.php，则可以利用文件内容读取 config.php中的$flag，

之前全局搜索flag审计到的config.php

<?php
	$config['hostname'] = '127.0.0.1';
	$config['username'] = 'root';
	$config['password'] = '';
	$config['database'] = '';
	$flag = '';
?>

重定向update.php

<?php
	require_once('class.php');
	if($_SESSION['username'] == null) {
		die('Login First');	
	}
	if($_POST['phone'] && $_POST['email'] && $_POST['nickname'] && $_FILES['photo']) {

		$username = $_SESSION['username'];
		if(!preg_match('/^\d{11}$/', $_POST['phone']))
			die('Invalid phone');

		if(!preg_match('/^[_a-zA-Z0-9]{1,10}@[_a-zA-Z0-9]{1,10}\.[_a-zA-Z0-9]{1,10}$/', $_POST['email']))
			die('Invalid email');
		
		if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
			die('Invalid nickname');

		$file = $_FILES['photo'];
		if($file['size'] < 5 or $file['size'] > 1000000)
			die('Photo size error');

		move_uploaded_file($file['tmp_name'], 'upload/' . md5($file['name']));
		$profile['phone'] = $_POST['phone'];
		$profile['email'] = $_POST['email'];
		$profile['nickname'] = $_POST['nickname'];
		$profile['photo'] = 'upload/' . md5($file['name']);

		$user->update_profile($username, serialize($profile));
		echo 'Update Profile Success!<a href="profile.php">Your Profile</a>';
	}
	else {
?>

传四个参数，phone，email，nickname，以及photo。
进行正则表达式的过滤，赋予到$profile变量中。

然后这里很重要的整理思路是，反序列化入口是profile，我们利用nickname带入数据，进而带入profile，最后反序列化利用

观察到serialize函数，序列化入口就是$profile

跟进文件包含的class.php

反序列化字符逃逸

审计class.php

<?php
require('config.php');

class user extends mysql{
	private $table = 'users';

	public function is_exists($username) {
		$username = parent::filter($username);

		$where = "username = '$username'";
		return parent::select($this->table, $where);
	}
	public function register($username, $password) {
		$username = parent::filter($username);
		$password = parent::filter($password);

		$key_list = Array('username', 'password');
		$value_list = Array($username, md5($password));
		return parent::insert($this->table, $key_list, $value_list);
	}
	public function login($username, $password) {
		$username = parent::filter($username);
		$password = parent::filter($password);

		$where = "username = '$username'";
		$object = parent::select($this->table, $where);
		if ($object && $object->password === md5($password)) {
			return true;
		} else {
			return false;
		}
	}
	public function show_profile($username) {
		$username = parent::filter($username);

		$where = "username = '$username'";
		$object = parent::select($this->table, $where);
		return $object->profile;
	}
	public function update_profile($username, $new_profile) {
		$username = parent::filter($username);
		$new_profile = parent::filter($new_profile);

		$where = "username = '$username'";
		return parent::update($this->table, 'profile', $new_profile, $where);
	}
	public function __tostring() {
		return __class__;
	}
}

class mysql {
	private $link = null;

	public function connect($config) {
		$this->link = mysql_connect(
			$config['hostname'],
			$config['username'], 
			$config['password']
		);
		mysql_select_db($config['database']);
		mysql_query("SET sql_mode='strict_all_tables'");

		return $this->link;
	}

	public function select($table, $where, $ret = '*') {
		$sql = "SELECT $ret FROM $table WHERE $where";
		$result = mysql_query($sql, $this->link);
		return mysql_fetch_object($result);
	}

	public function insert($table, $key_list, $value_list) {
		$key = implode(',', $key_list);
		$value = '\'' . implode('\',\'', $value_list) . '\''; 
		$sql = "INSERT INTO $table ($key) VALUES ($value)";
		return mysql_query($sql);
	}

	public function update($table, $key, $value, $where) {
		$sql = "UPDATE $table SET $key = '$value' WHERE $where";
		return mysql_query($sql);
	}

	public function filter($string) {
		$escape = array('\'', '\\\\');
		$escape = '/' . implode('|', $escape) . '/';
		$string = preg_replace($escape, '_', $string);

		$safe = array('select', 'insert', 'update', 'delete', 'where');
		$safe = '/' . implode('|', $safe) . '/i';
		return preg_replace($safe, 'hacker', $string);
	}
	public function __tostring() {
		return __class__;
	}
}
session_start();
$user = new user();
$user->connect($config);

filter过滤（利用点）

    public function filter($string) {
        $escape = array('\'', '\\\\');
        $escape = '/' . implode('|', $escape) . '/';
        $string = preg_replace($escape, '_', $string);

        $safe = array('select', 'insert', 'update', 'delete', 'where');
        $safe = '/' . implode('|', $safe) . '/i';
        return preg_replace($safe, 'hacker', $string);
    }

利用where替换hacker五个字符逃逸出34个";}s:5:"photo";s:10:"config.php";}字符

使其从nickname逃逸到photo，从nickname逃逸出，"};将前面的nickname数组闭合之后，剩下的s:5:“photo”;s:10:“config.php”;}就会被当作photo的部分了，至于后面的upload，由于被后面";}结束反序列化，也就被丢弃，这样就实现了config.php的读取

同时由于对nickname的长度限制，用数组绕过

if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
			die('Invalid nickname');

码农公寓

[MRCTF2020]PYWebsite

[0CTF 2016]piapiapia

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