- 前言 -
SSRF绕过的一种思路，就是利用DNS重绑定，它也被广泛用于绕过同源策略，本质就是欺骗客户端请求的IP地址。
但是之前都是用如xip.io等别人搭建好的平台去利用，没有自己搞过，也没能彻底理解其中的原理
- DNS重绑定 -
浏览网页过程中，用户在地址栏中输入包含域名的网址，浏览器通过DNS服务器将域名解析为IP地址，然后向对应的IP地址请求资源，最后展现给用户。即 域名 => 公共DNS服务器 => IP
但是作为域名的所有者，可以随时设置解析IP，举例如下：
用户第一次访问，解析域名test.gm7.org的IP为104.21.26.222
在用户第二次访问前，修改域名解析的IP为127.0.0.1
用户第二次访问，解析域名test.gm7.org的IP为127.0.0.1
[!tip]
一般来说我们的操作系统默认能够将DNS返回来的这个IP地址信息保存60秒，而超过60秒后如果需要再次访问这个域名，就会重新去请求一次dns
对于浏览器来说，两次访问的都是同一域名，是符合浏览器的同源策略的，但是第二次访问解析到其他IP，调用到了其他资源。这样的行为被称之为域名重新绑定攻击（DNS ReBinding）。
[!tip]
简而言之：当我们发起域名解析请求的时候,第一次访问会返回一个ip地址A，但是当我们发起第二次域名解析请求的时候，却会返回一个不同于A的ip地址B。
- 实现方法 -
ceye
ceye.io个人信息最下方，可以设置解析IP，具体说明：http://ceye.io/dns-rebinding
有一个注意点：就是每次都是随机返回一个设置的IP，所以可能大概率碰运气
验证：
重绑定使用域名：r.abcdef.ceye.io or *.r.abcdef.ceye.io
基础自建
前提是有域名，然后增加一个A记录和一个NS记录
此时访问dra.gm7.org域名，先解析该域名的DNS域名为dr.gm7.org，指向10开头的这台服务器。
在10开头的这台服务器上，运行如下python脚本
[!tip]
在ubuntu中，可能会遇到53端口被占用情况，可以尝试
service systemd-resolved stop
service named stop
# pip2 install twisted
# sudo python2 thiss.py
from twisted.internet import reactor, defer
from twisted.names import client, dns, error, server
record={}
class DynamicResolver(object):
def _doDynamicResponse(self, query):
name = query.name.name
if name notin record or record[name]<1:
ip ="114.114.114.114"
else:
ip ="127.0.0.1"
if name notin record:
record[name] =0
record[name] +=1
print name +" ===> "+ ip
answer = dns.RRHeader(
name = name,
type = dns.A,
cls = dns.IN,
ttl =0,
payload = dns.Record_A(address = b'%s'% ip, ttl=0)
)
answers = [answer]
authority = []
additional = []
return answers, authority, additional
def query(self, query, timeout=None):
return defer.succeed(self._doDynamicResponse(query))
def main():
factory = server.DNSServerFactory(
clients=[DynamicResolver(), client.Resolver(resolv='/etc/resolv.conf')]
)
protocol = dns.DNSDatagramProtocol(controller=factory)
reactor.listenUDP(53, protocol)
reactor.run()
if__name__=='__main__':
raiseSystemExit(main())
singularity
A DNS rebinding attack framework. https://github.com/nccgroup/singularity
wiki: https://github.com/nccgroup/singularity/wiki
主要针对绕过SOP，也可用于绕过SSRF
安装配置
[!note]
也需要一个域名，域名配置和上面自建一样，一个A记录一个NS记录
安装：需要go环境
git clone https://github.com/nccgroup/singularity
cd singularity/cmd/singularity-server
go build
部署web界面：
给二进制文件移动到html目录同级
直接运行二进制文件即可启动
访问管理页面：8080端口
基础使用
进入管理页面，输入参数，开始攻击后拿到域名
multiple answers策略设置下的效果
其他Rebinding Strategy说明见下方，在multiple answers策略下，浏览器会拿到多个dns响应，首先会尝试用第一个连接，失败之后就会尝试另一个，这时就实现了DNS重绑定。这个其实算是一个正常功能，也非常常见，可以说是DNS层面的负载均衡技术。
Manager UI说明
manager web界面是配置和启动DNS重新绑定攻击的地方。默认情况下，它监听端口8080。下表介绍了管理器界面中的所有表单字段和按钮：
|
Field Name |
Description |
|
Attack Host Domain |
This is the (sub-)domain where the Singularity web server is running. Default value: d.rebind.it |
|
Attack Host |
This is the IP address where the manager and the attack payloads are hosted. Default value: xxx.xxx.xxx.xxx |
|
Target Host |
This is the IP address or FQDN (e.g. jenkins.internal.target.com) of the target system where the victim (target) application is running. Default value: 127.0.0.1 |
|
Target Port |
This is the port where the victim (target) application is listening on. Default value: 8080 |
|
Request New Port |
This will request Singularity to listen on a new port. This feature is only available when Singularity has been started with the -dangerouslyAllowDynamicHTTPServers command line option. |
|
Attack Payload |
This is where you select the payload, i.e. which application you are trying to exploit. |
|
Start Attack |
Start the DNS rebinding attack. Be patient and wait for at least one minute. Open the browser web console to see debugging logs. |
|
Toggle Advanced Options |
This button will enable the advanced fields described below. |
|
Rebinding Strategy |
Specify how to respond to DNS queries from a victim client. The following options are available: * First then second (default, conservative): This is the default value. It should work on most if not all platforms in 40 to 60 seconds. |
|
Interval |
How long to wait between connection attempts to the target application in seconds. Default value: 20 |
|
Flood DNS Cache |
Perform ~1000 DNS queries to evict cached DNS entries in Google Chrome and to improve DNS rebind attack speed from ~60s down to ~20s. Useful with the following DNS rebinding strategies: First then second, Round robin, Random. Default value: unset |
|
Index Token |
The index token is used by Singularity to detect if the rebinding has happened yet. Default value: thisismytesttoken. |
参考文章
•从0到1认识DNS重绑定攻击
•abusing-dns-browser-based-port-scanning-and-dns-rebinding
•DNS Rebinding in Browser
原文始发于微信公众号（安全宇宙）：【创宇小课堂】渗透测试-DNS重绑定
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