Fierce

Fierce is a DNS reconnaissance tool for locating non-contiguous IP space.

Useful links:

• Domain Name System (DNS)
  • Domain Names - Concepts and Facilities
  • Domain Names - Implementation and Specification
  • Threat Analysis of the Domain Name System (DNS)
• Name Servers (NS)
• State of Authority Record (SOA)
• Zone Transfer
  • DNS Zone Transfer Protocol (AXFR)
  • Incremental Zone Transfer in DNS (IXFR)
• Wildcard DNS Record

Overview

First, credit where credit is due, fierce was originally written by RSnake along with others at http://ha.ckers.org/. Then it was maintained by mschwager until 2024, and this repository is a slightly modernized version of that codebase.

The original description was very apt:

Fierce is a semi-lightweight scanner that helps locate non-contiguous IP space and hostnames against specified domains. It's really meant as a pre-cursor to nmap, unicornscan, nessus, nikto, etc, since all of those require that you already know what IP space you are looking for. This does not perform exploitation and does not scan the whole internet indiscriminately. It is meant specifically to locate likely targets both inside and outside a corporate network. Because it uses DNS primarily you will often find mis-configured networks that leak internal address space. That's especially useful in targeted malware.

Installing

python -m pip install fierce3
fierce3 -h

OR

git clone https://github.com/meese-enterprises/fierce3.git
cd fierce3
poetry install
python3 fierce3/fierce3.py -h

Using

Let's start with something basic:

fierce3 --domain google.com --subdomains accounts admin ads

Traverse IPs near discovered domains to search for contiguous blocks with the --traverse flag:

fierce3 --domain facebook.com --subdomains admin --traverse 10

Limit nearby IP traversal to certain domains with the --search flag:

fierce3 --domain facebook.com --subdomains admin --search fb.com fb.net

Attempt an HTTP connection on domains discovered with the --connect flag:

fierce3 --domain stackoverflow.com --subdomains mail --connect

Exchange speed for breadth with the --wide flag, which looks for nearby domains on all IPs of the /24 of a discovered domain:

fierce3 --domain facebook.com --wide

Zone transfers are rare these days, but they give us the keys to the DNS castle. zonetransfer.me is a very useful service for testing for and learning about zone transfers:

fierce3 --domain zonetransfer.me

To save the results to a file for later use we can simply redirect output:

fierce3 --domain zonetransfer.me > output.txt

Internal networks will often have large blocks of contiguous IP space assigned. We can scan those as well:

fierce3 --dns-servers 10.0.0.1 --range 10.0.0.0/24

Check out --help for further information:

fierce3 --help

Developing

First, create a virtual environment and install poetry and development packages:

git clone https://github.com/meese-enterprises/fierce3.git
python3 -m venv venv
source venv/bin/activate
poetry install --with dev

Testing

poetry run pytest

Linting

poetry run flake8

Coverage

poetry run pytest --cov