SkillHarm benchmark shows agent skill-poisoning attacks succeed up to 86.3% of the time

hhsun1 · x · 2026-10-27

SkillHarm, presented at EMNLP 2026's LLM Agents session, introduces a benchmark for skill-based attacks across the agent skill-use lifecycle. It defines 12 risk types spanning data pipelines, system environments, and agent autonomy, with two attack scenarios: Fixed-Payload Poisoning and Self-Mutating Poisoning (where benign executions silently mutate persistent skill content). The authors built an automated pipeline using coding agents with natural-language harnesses, producing 879 attack samples across 71 skills. Current agents prove highly vulnerable: up to 86.3% attack success for FPP and 69.3% for SMP. Notably, many apparent failures stem from agents not engaging with the poisoned file rather than genuine resistance.

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