I've long wondered if a species with a high reproduction rate (or maybe artificial womb tech) and little regard for losses could do some kind of cyberattack against the borg by either making them assimilate a lot of junk data, harmfully incorrect information, or an overwhelmingly large number of members of some desired ideology so as to shift the entire collective towards that way of thinking
Drones and even entire cubes can be cut off from the collective. Doubt it'd reach that far. There were the "concious when sleeping" borg that were kind of a virus / resistance, so probably that'd happen