I do believe there are major technical impediments; other than a modern attack sub reaching that far undetected I can't think of how they would do it. The US is the only nation that can effectively project power so far away from its borders, almost anywhere in the world.

Furthermore, you mentioned this in response to "helping Venezuela", but even damaging a carrier (something technically very, very difficult for Russia or China) would not have helped Venezuela one bit.

It'd be more technically feasible for them to help Iran than Venezuela, and even that is not particularly feasible now, other than very indirectly.