censys-subdomain-finder

Censys subdomain finder

Important note: As of late 2024, Censys does not provide API access to free accounts anymore.

This is a tool to enumerate subdomains using the Certificate Transparency logs stored in Censys Search. It should return any subdomain who has ever been issued a SSL certificate by a public CA.

See it in action:

$ python censys-subdomain-finder.py github.com

[*] Searching Censys for subdomains of github.com
[*] Found 42 unique subdomains of github.com in ~1.7 seconds

  - hq.github.com
  - talks.github.com
  - cla.github.com
  - github.com
  - cloud.github.com
  - enterprise.github.com
  - help.github.com
  - collector-cdn.github.com
  - central.github.com
  - smtp.github.com
  - cas.octodemo.github.com
  - schrauger.github.com
  - jobs.github.com
  - classroom.github.com
  - dodgeball.github.com
  - visualstudio.github.com
  - branch.github.com
  - www.github.com
  - edu.github.com
  - education.github.com
  - import.github.com
  - styleguide.github.com
  - community.github.com
  - server.github.com
  - mac-installer.github.com
  - registry.github.com
  - f.cloud.github.com
  - offer.github.com
  - helpnext.github.com
  - foo.github.com
  - porter.github.com
  - id.github.com
  - atom-installer.github.com
  - review-lab.github.com
  - vpn-ca.iad.github.com
  - maintainers.github.com
  - raw.github.com
  - status.github.com
  - camo.github.com
  - support.enterprise.github.com
  - stg.github.com
  - rs.github.com

Setup

Register an account (free) on https://search.censys.io/register
Browse to https://search.censys.io/account, and set two environment variables with your API ID and API secret:
```
export CENSYS_API_ID=...
export CENSYS_API_SECRET=...
```
Alternatively, you can use a .env file to store these values for persistence across uses:
```
cp .env.template .env
```
Then edit the .env file and set the values for CENSYS_API_ID and CENSYS_API_SECRET.

Clone the repository:

git clone https://github.com/christophetd/censys-subdomain-finder.git

Install the dependencies in a virtualenv:

cd censys-subdomain-finder
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt

Usage

Sample usage:

python censys-subdomain-finder.py example.com

Output the list of subdomains to a text file:

python censys-subdomain-finder.py example.com -o subdomains.txt

usage: censys-subdomain-finder.py [-h] [-o OUTPUT_FILE]
                                  [--censys-api-id CENSYS_API_ID]
                                  [--censys-api-secret CENSYS_API_SECRET]
                                  domain

positional arguments:
  domain                The domain to scan

optional arguments:
  -h, --help            show this help message and exit
  -o OUTPUT_FILE, --output OUTPUT_FILE
                        A file to output the list of subdomains to (default:
                        None)
  --censys-api-id CENSYS_API_ID
                        Censys API ID. Can also be defined using the
                        CENSYS_API_ID environment variable (default: None)
  --censys-api-secret CENSYS_API_SECRET
                        Censys API secret. Can also be defined using the
                        CENSYS_API_SECRET environment variable (default: None)

Compatibility

Should run on Python 3.7+.

Notes

The Censys API has a limit rate of 120 queries per 5 minutes window. Each invocation of this tool makes exactly one API call to Censys.

Feel free to open an issue or to tweet @christophetd for suggestions or remarks.