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An audit of eleven agent-hijacking detector evaluations found attack rates nobody varies and almost no cross-benchmark testing

AspireAI community · arXiv
Detectors that flag hijacked agents from tool-call traces are usually evaluated on data where attacks make up 16% to 86% of test samples, and none of the eleven evaluations audited varies that share or tests on a second benchmark. On the AgentDrift and AgentDojo benchmarks the authors tested detectors reading tool identities, behavior, call sequences, step embeddings or text, alongside the released AlignmentCheck action monitor. At a 2% attack rate a detector with an AUROC of 0.879 reached precision 0.076, and the negative mix alone moved that precision between 0.039 and 0.117. Detector rankings cross near 50% tool coverage and reverse below it, because unseen tools map to inputs training never reached, and dropout on tool inputs largely removes that reversal. No detector trained on AgentDrift ranked AgentDojo traces better than chance (AUROC 0.47 to 0.52), including one that reached 0.996 within AgentDojo; the monitor trained on neither reached 0.930, but with its open backbone its released decision rule would still mostly raise false alerts at a 2% attack rate. The paper ends with a checklist for evaluating trace detectors rather than a new detector.
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