Hi Matteo,
Thanks for using our community!
What you can do to achieve this is create a search from the discover section of Kibana and export the CSV, where you will then be able to see all the IPs.
To do so follow these steps
1- On Kibana go to Discover
2- On the Discover page, press Add filter and create the filter: Field =
rule.id Operator=is and Value=Rule you want to filter in this example 23504

3- After getting the result at the top right of the screen you can modify the time you want to cover, then press Save to save the query.
4- Once Query is saved on the top right click Reporting and Generate CSV
This will download automatically the CSV Report when you open it on Excel you will be able to see the IP column and filter by it as seen below, You can then remove all unnecessary columns or copy and use this information.
Let me know if this covers your question
Regards!!