CtrlRAG: Black-box Adversarial Attacks Based on Masked Language Models in Retrieval-Augmented Language Generation

Abstract: Retrieval-Augmented Generation (RAG) systems enhance LLMs by integrating external knowledge bases. However, this integration introduces a new security threat: adversaries can exploit the retrieval mechanism to inject malicious content into the knowledge base, thereby influencing the generated responses. Based on this attack vector, we propose CtrlRAG, a novel attack method designed for RAG system in the black-box setting, which aligns with real-world scenarios. Unlike existing attack methods, CtrlRAG introduces a perturbation mechanism using Masked LLM (MLM) to dynamically optimize malicious content in response to changes in the retrieved context. Experimental results demonstrate that CtrlRAG outperforms three baseline methods in both Emotional Manipulation and Hallucination Amplification objectives. Furthermore, we evaluate three existing defense mechanisms, revealing their limited effectiveness against CtrlRAG and underscoring the urgent need for more robust defenses.