For some reason my brain went stupid on me and I cannot recall the rules for attacking other players in fedspace.

I think its ok if they are red, but not really certain.

Is there any provision for attacking someone parked in sector 1 with an ISS without provoking a fed response? And if not, what might that response be? I have not had occasion to do that in over a decade.

If they are red, or if they have exp >= 1000.

If they're in an iSS, they're prolly blue. If their exp is >= 1000, they can be attacked. Of course that means the attacking player might go red, and if they're in an ISS they might lose it when they warp out... so, all things to plan for if you're planning to do that.