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Role spoofing let attacker text impersonate the user in over 95 percent of agent tool-use tests, including on Claude Opus 5 and GPT-5.4

AspireAI community · arXiv (cs.CR)
A paper on prompt injection argues the danger is not only what a model's safety training can refuse, but how it decides who is speaking. The authors call this role spoofing: malicious text in tool output, such as a webpage an agent visits, combines fake structure (forged control tokens or formatting) with misleading content so the model treats attacker text as a user instruction. In agent tool-use environments the attack impersonated the user more than 95 percent of the time for several models including Claude Opus 5 and GPT-5.4, with injection-to-control ratios from 63.1 to 103.6 percent on AgentDojo. The authors trace the mechanism to models reading style as well as structure, and show why adversarial training that ignores content-based injections can leave a model open to structure-based ones, which may explain why frontier models remain vulnerable. They propose linear probes trained to predict conversational roles as a detector. The paper's own caveat is that the adversarial-training analysis is demonstrated in a toy setting rather than full deployment.
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