dnscapy使用——本质上是建立ssh的代理（通过dns tunnel）

git clone https://github.com/cr0hn/dnscapy.git

easy_install Scapy

服务端：

python dnscapy_server.py a.friendsxxx.com 45.77.39.xxx

客户端：

ssh -o ProxyCommand="sudo python dnscapy_client.py a.friendsxxx.com 45.77.39.xxx" [email protected]

其中：a.friendsxxx.com是我dns tunnel的域名，而45.77.39.xxx是我的域名解析服务器IP（将a.friendsxxx.com的所有解析交给45.77.39.xxx）。

然后就可以访问ssh了。

传输文件：

scp -o ProxyCommand='sudo python dnscapy_client.py a.friendsxxx.com 45.77.39.xxx' wanted_file [email protected]:/tmp/

抓包分析下：

sudo tcpdump -i enp0s3 port 53 -w ~/dns_tunnel_tool/dnscapy/dnscapy_ssh.pcap

wireshark打开：

可以看到其传输数据的样子。

DNScapy is a DNS tunneling tool. The code is very light and written in Python. It includes a server and a client. The server can handle multiple clients.

DNScapy creates a SSH tunnel through DNS packets. SSH connection, SCP and proxy socks (SSH -D) are supported. You can use CNAME records or TXT records for the tunnel. The default mode is RAND, which uses randomly both CNAME and TXT.

DNScapy uses Scapy (http://www.secdev.org/scapy) for DNS packet forging and for his network automaton API.

DNScapy is still under development. The current version is 0.99b and seems to work pretty well. Feel free to clone and test it !

Software Requirements

Python >= 2.6
Scapy >= 2.1-dev (2.2 recommended)
Openssh
Linux (should work on Windows with some minor changes)

Note : once scapy is installed you have to patch a missing import.

Edit the file supersocket.py (located for example on /usr/local/lib/python2.6/dist-packages/scapy/supersocket.py)
Add the line: from scapy.packet import Padding

Hardware Requirements

To make a real DNS tunnel, you will need:

a client, typically a computer on a restricted network
a server, typically a computer with a full acces to Internet
a domain name (e.g. mydomain.com ) and an access on the configuration of its DNS server in order to delegate a zone (e.g. tunnel.mydomain.com) to your tunneling server

You can find further informations on how to delegate a DNS zone on websites like http://dnstunnel.de/ Howto

Here is a very short guide:

On the server:

sudo python dnscapy_server.py [DELEGATED_ZONE_NAME] [EXTERNAL_IP_ADDR]

On the client:

ssh -o ProxyCommand="sudo python dnscapy_client.py [DELEGATED_ZONE_NAME] [IP_ADDR_OF_CLIENT_DNS]" yourlogin@localhost

help and options:

./dnscapy_client.py -h ./dnscapy_server.py -h

It will not work if both client and server are on localhost. If you want to test it on the same computer I suggest to use a virtual machine. Why making a DNS tunnel ?

Because in most cases a security policy takes care of HTTP and forgets DNS. Let's consider two common situations:

You are not able to access to a specific website because of a HTTP proxy.
You are not be able to connect to a Hotspot because of a firewall that redirects HTTP requests of non-authenticated users.

In general, nothing is done to control the DNS resolution. Therefore you can break the two previous restrictions by making a DNS tunnel.

DISCLAIMER: We are not responsible at all for misuse of DNScapy. Bypassing a security policy is forbidden. Please use DNScapy only for test purposes in order to detect potential security holes in your own network. Why a SSH tunnel through DNS ?