Any document store where you haven’t meticulously vetted each document— forget about actual bad actors— runs this risk. A size org across many years generates a lot of things. Analysis that were correct at one point and not at another, things that were simply wrong at all times, contradictory, etc.
You have to choose model suitably robust is capabilities and design prompts or various post training regimes that are tested against such, where the model will identify the different ones and either choose the correct one on surface both with an appropriately helpful and clear explanation.
At minimum you have to start from a typical model risk perspective and test and backtest the way you would traditional ML.
You're right, and this is an underappreciated point. The "attacker" framing can actually obscure the more common risk: organic knowledge base degradation over time. The poisoning attack is just the adversarial extreme of a problem that exists in every large document store.
The model robustness angle is valid but I'd push back slightly on it being sufficient as a primary control. The model risk / backtesting framing is exactly right for the generation side. Where RAG diverges from traditional ML is that the "training data" is mutable at runtime (any authenticated user or pipeline can change what the model sees without retraining).