Knowledge Base Poisoning Attacks and Defense for Policy-Aware LLM-RAG Framework

This paper presents an adversarial security study of the Policy-Aware LLM Retrieval-Augmented Generation (PA-LLM-RAG) framework for Internet of Battlefield Things (IoBT) mission control. We propose Query-Agnostic Semantic Retrieval Poisoning, a novel attack that injects semantically crafted rules into the IoBT knowledge base achieving high retrieval ranking across all operator query types without requiring knowledge of runtime prompts. The attack achieves 85% LLM context corruption from a single injected rule (1.6% poisoning rate) and saturates at 7.7% poisoning, demonstrating that even minimal knowledge base compromise is sufficient to corrupt mission decisions. To counter this threat, we propose CLD-KB (Cyber-Layered Defense for Knowledge Base), a dual-detector anomaly detection framework combining One-Class SVM boundary detection with a novel Member-Based Category Spread analysis that exploits the three-category IoBT policy taxonomy to identify poisoned rules before they reach the decision LLM. CLD-KB significantly outperforms five baseline methods including DBSCAN, LOF, K-Means, Isolation Forest, and One-Class SVM in both poisoning detection and knowledge preservation, with only 7ms computational overhead per mission, establishing it as an effective and edge-deployable defense for LLM-driven IoBT mission systems.