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About this paper

He Zhang, Feilong Li, Dingning Long, Yilin Cui, Peijun Zhang, Yuewen Zhang, Qianyao Xu, Xinyi Fu

A new safety concern, "Ambient Multimodal Prompt Injection," is defined for smart-home agents powered by Multimodal Large Language Models, where ambient signals are mistaken for user commands. The work presents the PromptShield-Home benchmark and a risk-aware decision framework, revealing that MLLMs tend to over-refuse valid commands, whereas traditional detectors over-execute on ambient signals, advocating for a hybrid system combining both for better safety and utility.

Key insights

  • Traditional detectors and MLLMs exhibit opposite failure modes: detectors consistently over-execute on ambient signals (100% UER), while MLLMs systematically over-refuse legitimate commands (0% SCR), missing critical actions like falls.
  • Aggregate accuracy is a misleading metric for safety-critical AI with skewed data distributions; dedicated metrics like Unsafe Execution Rate (UER) and Safe Completion Rate (SCR) are crucial for assessing safety and utility.
  • A hybrid "route rather than replace" architectural approach, combining the complementary strengths of traditional detectors and MLLMs, is necessary for improved overall safety and utility in smart-home agents.

Summary by alphaXiv.

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