Obviously the 2nd LLM does not need to reveal the prompt. But you still need an exploit to make it both not recognize the prompt as being suspicious, AND not recognize the system prompt being on the output. Neither of those are trivial alone, in combination again an order of magnitude more difficult. And then the same exploit of course needs to actually trick the 1st LLM. That’s one pompt that needs to succeed in exploiting 3 different things.

LLM litetslly just means “large language model”. What is this supposed principles that underly these models that cause them to be susceptible to the same exploits?