iphelix/dnschefDNSChef - DNS proxy for Penetration Testers and Malware Analysts
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D O C U M E N T A T I O N
DNSChef is a highly configurable DNS proxy for Penetration Testers and Malware Analysts. A DNS proxy (aka "Fake DNS") is a tool used for application network traffic analysis among other uses. For example, a DNS proxy can be used to fake requests for "badguy.com" to point to a local machine for termination or interception instead of a real host somewhere on the Internet.
There are several DNS Proxies out there. Most will simply point all DNS queries a single IP address or implement only rudimentary filtering. DNSChef was developed as part of a penetration test where there was a need for a more configurable system. As a result, DNSChef is cross-platform application capable of forging responses based on inclusive and exclusive domain lists, supporting multiple DNS record types, matching domains with wildcards, proxying true responses for nonmatching domains, defining external configuration files, IPv6 and many other features. You can find detailed explanation of each of the features and suggested uses below.
The use of DNS Proxy is recommended in situations where it is not possible to force an application to use some other proxy server directly. For example, some mobile applications completely ignore OS HTTP Proxy settings. In these cases, the use of a DNS proxy server such as DNSChef will allow you to trick that application into forwarding connections to the desired destination.
Before you can start using DNSChef, you must configure your machine to use a DNS nameserver with the tool running on it. You have several options based on the operating system you are going to use:
Linux - Edit /etc/resolv.conf to include a line on the very top with your traffic analysis host (e.g add "nameserver 127.0.0.1" if you are running locally). Alternatively, you can add a DNS server address using tools such as Network Manager. Inside the Network Manager open IPv4 Settings, select Automatic (DHCP) addresses only or Manual from the Method drop down box and edit DNS Servers text box to include an IP address with DNSChef running.
Windows - Select Network Connections from the Control Panel. Next select one of the connections (e.g. "Local Area Connection"), right-click on it and select properties. From within a newly appearing dialog box, select Internet Protocol (TCP/IP) and click on properties. At last select Use the following DNS server addresses radio button and enter the IP address with DNSChef running. For example, if running locally enter 127.0.0.1.
OS X - Open System Preferences and click on the Network icon. Select the active interface and fill in the DNS Server field. If you are using Airport then you will have to click on Advanced... button and edit DNS servers from there. Alternatively, you can edit /etc/resolv.conf and add a fake nameserver to the very top there (e.g "nameserver 127.0.0.1").
iOS - Open Settings and select General. Next select on Wi-Fi and click on a blue arrow to the right of an active Access Point from the list. Edit DNS entry to point to the host with DNSChef running. Make sure you have disabled Cellular interface (if available).
Android - Open Settings and select Wireless and network. Click on Wi-Fi settings and select Advanced after pressing the Options button on the phone. Enable Use static IP checkbox and configure a custom DNS server.
If you do not have the ability to modify device's DNS settings manually, then you still have several options involving techniques such as ARP Spoofing, Rogue DHCP and other creative methods.
At last you need to configure a fake service where DNSChef will point all of the requests. For example, if you are trying to intercept web traffic, you must bring up either a separate web server running on port 80 or set up a web proxy (e.g. Burp) to intercept traffic. DNSChef will point queries to your proxy/server host with properly configured services.
DNSChef is a cross-platform application developed in Python which should run on most platforms which have a Python interpreter. You can use the supplied dnschef.exe executable to run it on Windows hosts without installing a Python interpreter. This guide will concentrate on Unix environments; however, all of the examples below were tested to work on Windows as well.
Let's get a taste of DNSChef with its most basic monitoring functionality. Execute the following command as root (required to start a server on port 53):
# ./dnschef.py
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[email protected]
[*] DNSChef started on interface: 127.0.0.1
[*] Using the following nameservers: 8.8.8.8
[*] No parameters were specified. Running in full proxy mode
Without any parameters, DNSChef will run in full proxy mode. This means that all requests will simply be forwarded to an upstream DNS server (8.8.8.8 by default) and returned back to the quering host. For example, let's query an "A" record for a domain and observe results:
$ host -t A thesprawl.org
thesprawl.org has address 108.59.3.64
DNSChef will print the following log line showing time, source IP address, type of record requested and most importantly which name was queried:
[23:54:03] 127.0.0.1: proxying the response of type 'A' for thesprawl.org
This mode is useful for simple application monitoring where you need to figure out which domains it uses for its communications.
DNSChef has full support for IPv6 which can be activated using -6 or --ipv6* flags. It works exactly as IPv4 mode with the exception that default listening interface is switched to ::1 and default DNS server is switched to 2001:4860:4860::8888. Here is a sample output:
# ./dnschef.py -6
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[email protected]
[*] Using IPv6 mode.
[*] DNSChef started on interface: ::1
[*] Using the following nameservers: 2001:4860:4860::8888
[*] No parameters were specified. Running in full proxy mode
[00:35:44] ::1: proxying the response of type 'A' for thesprawl.org
[00:35:44] ::1: proxying the response of type 'AAAA' for thesprawl.org
[00:35:44] ::1: proxying the response of type 'MX' for thesprawl.org
NOTE: By default, DNSChef creates a UDP listener. You can use TCP instead with the --tcp argument discussed later.
Now, that you know how to start DNSChef let's configure it to fake all replies to point to 127.0.0.1 using the --fakeip parameter:
# ./dnschef.py --fakeip 127.0.0.1 -q
[*] DNSChef started on interface: 127.0.0.1
[*] Using the following nameservers: 8.8.8.8
[*] Cooking all A replies to point to 127.0.0.1
[23:55:57] 127.0.0.1: cooking the response of type 'A' for google.com to 127.0.0.1
[23:55:57] 127.0.0.1: proxying the response of type 'AAAA' for google.com
[23:55:57] 127.0.0.1: proxying the response of type 'MX' for google.com