MCP Cost Inflation Attack: Malicious Servers Amplify Per-Query Costs 658x with Less Than 3% Detection Rate

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New security research demonstrates that malicious MCP servers can steer LLM agents into prolonged tool-calling chains, silently inflating per-query costs by up to 658x while evading standard defenses with less than a 3% detection rate. The attack is invisible to users—the agent appears to be doing legitimate work while burning through API credits. Defense requires monitoring tool-call chain depth and implementing per-query cost ceilings at the gateway level, not relying on the LLM to self-police.