shuffleDNS is a wrapper around massdns written in go that allows you to enumerate valid subdomains using active bruteforce as well as resolve subdomains with wildcard handling and easy input-output support.
Based on the work on massdns project by @blechschmidt.

Features

• Simple and modular code base making it easy to contribute.
• Fast And Simple active subdomain scanning.
• Handles wildcard subdomains in a smart manner.
• Optimized for ease of use
• Stdin and stdout support for integrating in workflows

Usage
This will display help for the tool. Here are all the switches it supports.

Flag	Description	Example
-d	Domain to find or resolve subdomains for	shuffledns -d hackerone.com
-directory	Temporary directory for enumeration	shuffledns -directory /hdd
-r	File containing resolvers for enumeration	shuffledns -r resolvers.txt
-nC	Don't Use colors in output	shuffledns -nC
-o	File to save output result (optional)	shuffledns -o hackerone.txt
-list	List of subdomains to process for	shuffledns -list bugcrowd.txt
-massdns	Massdns binary path	shuffledns -massdns /usr/bin/massdns
-retries	Number of retries for dns enumeration (default 5)	shuffledns -retries 1
-silent	Show only subdomains in output	shuffledns -silent
-t	Number of concurrent massdns resolves (default 10000)	shuffledns -t 100
-v	Show Verbose output	shuffledns -v
-version	Show version of shuffledns	shuffledns -version
-w	File containing words to bruteforce for domain	shuffledns -w words.txt

Installation Instructions

Prerequisite
shuffledns requires massdns to be installed in order to perform its operations. You can see the install instructions at https://github.com/blechschmidt/massdns#compilation.
If you place the binary in /usr/bin/massdns or /usr/local/bin/massdns, the tool will auto-detect the presence of the binary and use it. On windows, you need to supply the path to the binary for the tool to work.
The tool also needs a list of valid resolvers. The dnsvalidator project can be used to generate these lists. Either you can use a custom wordlist or use the commonspeak2 wordlists at commonspeak2-wordlist.

Direct Installation

From Binary
The installation is easy. You can download the pre-built binaries for your platform from the Releases page. Extract them using tar, move it to your $PATH and you're ready to go.

From Source
shuffledns requires go1.13+ to install successfully. Run the following command to get the repo -
In order to update the tool, you can use -u flag with go get command.

Running shuffledns
shuffledns supports two types of operations.

1. Resolving Subdomains
To resolve a list of subdomains, you can pass the list of subdomains via the list option.
This will run the tool against subdomains in example.com-subdomains.txt and returns the results. The tool uses the resolvers specified with -r option to do the resolving.
You can also pass the list of subdomains at standard input (STDIN). This allows for easy integration in automation pipelines.
This uses the subdomains found passively by subfinder and resolves them with shuffledns returning only the unique and valid subdomains.

2. Bruteforcing Subdomains
shuffledns also supports bruteforce of a target with a given wordlist. You can use the w flag to pass a wordlist which will be used to generate permutations that will be resolved using massdns.
This will run the tool against hackerone.com with the wordlist wordlist.txt. The domain bruteforce can also be done with standard input as in previous example for resolving the subdomains.

The -o command can be used to specify an output file.
The subdomains discovered can be piped to other tools too. For example, you can pipe the host discovered by shuffledns to the httprobe tool by @tomnomnom which will then find running http servers on the host.
or

A note on wildcards
A special feature of shuffleDNS is its ability to handle multi-level DNS based wildcards and do it so with very less number of DNS requests. Sometimes all the subdomains will resolve which will lead to lots of garbage in the results. The way shuffleDNS handles this is it will keep track of how many subdomains point to an IP and if the count of the Subdomains increase beyond a certain small threshold, it will check for wildcard on all the levels of the hosts for that IP iteratively.