Sublert is a security and reconnaissance tool which leverages certificate transparency to automatically monitor new subdomains deployed by specific organizations and issued TLS/SSL certificate.

The tool is supposed to be scheduled to run periodically at fixed times, dates, or intervals (Ideally each day). New identified subdomains will be sent to Slack workspace with a notification push. Furthermore, the tool performs DNS resolution to determine working subdomains.


  • Virtual Private Server (VPS) running on Unix. (I personally use digitalOcean)
  • Python 2.x or 3.x.
  • Free Slack workspace.

Also Read – AutoRDPwn : The Shadow Attack Framework

How to set up?


  • Virtual Private Server (VPS) running on Unix. (I use digitalOcean)
  • Python 2.x or 3.x.
  • Free Slack workplace.

First of all, you will have to clone the tool from Github to your web server:

$ git clone && cd sublert

Now, we can install the required modules as follows:

forPython 2:

$ sudo pip install -r requirements.txt

alternatively, Python 3:

$ sudo pip3 install -r requirements.txt

Next step is to create a Slack workplace to where new subdomains will be sent to. Just browse to and create a free account.

Then, create two channels: one for the subdomains and the other is for error logging as follows:

Next, we need to generate Webhook URLs for each channel so we can leverage Slack API.

Browse to and create a new application.

Browse to Incoming Webhooks and create two Webhooks and link each one to the two channels formed previously.

And link each webhook with the corresponding Slack channel.

You will obtain a link in the following format:

Copy both two webhook links and edit

You’re almost ready! Interesting part now is adding domains to monitor for new subdomains. For now, it’s preferable to add each domain separately. Let’s add PayPal for instance:

$ python -u

You can proceed the same way with all the other domain names you would like to monitor. Once you’re finished adding the targets, the next step would be to configure Cron in order to schedule execution of Sublert periodically at fixed times.

Let’s make executable:

$ chmod u+x

Now, we need to add a new Cron job to schedule execution of it at given time. To do it, type:

$ Crontab -e

Add the following line at the end of the Cron file:

0 */12 * * * cd /root/sublert/ && /usr/bin/python -r -l >> /root/sublert/sublert.log 2>&1

You will need to change /root/sublert/ to the exact directory where you have the tool.

If you’re using python3 make sure to change /usr/bin/python to /usr/bin/python3

  • 0 */12 * * * → instructs Cron to run the tool every 12th hour. If you wish to change it to any fixed time you want, feel free to use to customize your timing.
  • -r → instructs Sublert to perform DNS resolution. It’s optional but recommended.
  • – l → instructs Sublert to log errors and push them to Slack channel. It’s optional but recommended.
  • /var/log/sublert.log 2>&1 → Instructs Cron to save Sublert output to /var/log/sublert.log which you can inspect at any given time if you have any doubts the tool is running smoothly.


Short FormLong FormDescription
-u–urlAdds a domain to monitor. E.g:
-d–deleteDomain to remove from the monitored list. E.g:
-a–listListing all monitored domains.
-t–threadsNumber of concurrent threads to use (Default: 20).
-r–resolvePerform DNS resolution.
-l–loggingEnable Slack-based error logging.
-m–resetReset everything.