DDHvi wrote:Infrastructure is what allows value creation and distribution. MALIGN showed they understood that by the Oyster Bay attack, which was primarily limited to the interstellar and orbital military INF.

How susceptible is Honorverse INF in general be to some sort of terrorist type attack? We have some of that with the OFS using local terrorists when Manticore found the new wormhole.
What if MALIGN has a puppet terrorist organization which has not yet been seen. With inexpensive contragravity, and hopefully hardened electronics being common, they might be in less danger than our current society (which routinely ships foods over thousands of miles) is to something like an EMP strike. But are they? And what other possibilities are there?
It wouldn't need to be MALIGN, whose aim is control. What would happen if some organization was like ISIS, wanting to return society to an earlier time, thus not caring about INF destruction, or even preferring to destroy it?
Well, in the Honorverse, nukes don't need fissionables or radiologicals - just a powerful enough gravity field will do. It appears from a nuke missile, that a multi-megaton device can easily be built which is the size of a major household appliance. Beyond the detection of the power source, there would be no way to track a nuke capable of eviscerating a large city.
In Storm from the Shadows, we saw a 40Mton nuke snuck into a medium sized (for the Honorverse) space station and it destroyed the entire structure and it's 40,000 inhabitants.
Now, how easy is it to acquire a nuke? pirates have them - they are not cheap, but pirates do have them and can replenish them, so Destroyer and Cruiser class warheads are sold on an active gray/black market. Smaller devices are used for demolition and construction purposes as evidenced by Torch of Freedom, and probably much easier to acquire in even larger numbers than missile warheads.
As you said, electronics and infrastructure in the future will most likely be more hardened than now, so EMPs should be less dangerous.