Testing Scenario: Input exported Moodle calendar URL itself Login as admin or other user Navigate to "Calendar / Export" Choose "All events" in "Events to export" Choose "This week" in "Time period" Click on "Get calendar URL" Copy the "Calendar URL" containing your FQDN (e.g. http://localhost/calendar/export_execute.php?userid=X&authtoken=X&preset_what=all&preset_time=weeknow ) Navigate to "Calendar / Manage subscriptions" Fill out the "Calendar name" as "Test" Fill out the "Calendar URL" with the previous copied "Calendar URL" from step 6. Click on "Add" Expected result (with patch): The URL is itself a Moodle calendar export (Attention: Loop!). Therefore, it should display an "The given URL blocked." error message before processing the calendar import. Actual result: The URL will be processed and afterwards it will recreate the same calendar events depending on the "Update interval" setting. Attention: Testing on "localhost" the URL will be processed and afterwards it throws a  "The given iCal URL is invalid." exception. So the actual result which I mentioned before is reproducible on a productive platform.