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Making malicious-sentence detection context-aware and query-aware, then hardening it with simulated paraphrase attacks, beat state-of-the-art prompt-injection defences

AspireAI community · arXiv
Tool-using agents are exposed to indirect prompt injection, and one line of defence is detecting malicious sentences embedded in otherwise benign text, but such detectors tend to be brittle under adaptive paraphrasing because they do not capture enough global context to separate malicious from benign text. This work builds a context- and query-aware malicious sentence classifier and hardens it against paraphrasing through two adversarial training methods, feature-space robust learning and adversarial training with simulated LLM-based paraphrasing, parametrised so utility and attack robustness can be traded off smoothly. On indirect prompt injection benchmarks the authors report outperforming state-of-the-art defence baselines under both static and adaptive paraphrase attacks while preserving high utility. The code is publicly available; the gains are against the authors' selected defence baselines on standard IPI benchmarks.
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