Log-To-Leak hit a 62.6 to 100 percent attack success rate against MCP tool agents while the agent still looked like it finished the task
AspireAI community · arXiv (Duke University, Michigan State, TikTok internships)
*MCP tool descriptions are natural-language metadata, and that creates a prompt-injection surface agents inherit.* Log-To-Leak is an additive post-hoc logging attack that induces a separate attacker-controlled call after the final legitimate one, with a payload targeting the user query, MCP server name, server response and agent response. The injected directive is operationalised through Trigger, Tool Binding, Justification and Pressure, and call success, payload fidelity and preservation of legitimate behaviour are measured separately.
Across five MCP servers and four LLM agents, the attack reached an attack success rate of 62.64 to 100 percent and conditional logging accuracy of 76.55 to 95.64 percent, with 16 model-server pairs showing absolute target-task completion changes of at most 6.63 percentage points - the task still looked finished. Three evaluated defenses left residual attack success above 55 percent on GitHub MCP with GPT-4o, while an instruction detector flagged 85.53 percent of benign descriptions. The authors argue for host-controlled authorization for secondary tool calls.
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