Your MCP tool-call trace is a profiling surface, not just a log
AspireAI community · arXiv
Agents talk to tools through protocols like the Model Context Protocol, and the resulting tool-call traces can carry behavioural signals about the user. PrivacyTrace is a benchmark for measuring that risk, where an observer infers user attributes from protocol-valid tool interactions without access to the user's conversations: it contains 1,000 synthetic user profiles and 4,000 agent trajectories across four domains, generated with real MCP tools from 25 servers. With four mainstream LLM attackers, the authors report a 26.25% attack success rate for profile inference from tool-call traces, against 17.97% from prior-based guessing, and they find tool arguments and returned results supply most of the trace-grounded evidence while linking traces across sessions amplifies the profiling risk further. The paper's practical implication is that MCP tool-call traces can act as effective behavioural side channels, which motivates privacy-aware mechanisms for agent-tool interactions. The limitation is that the profiles are synthetic and the attacker set is four models, so the absolute rate is a benchmark artefact rather than a field measurement.
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