MCP Pitfall Lab: Exposing Developer Pitfalls in MCP Tool Server Security under Multi-Vector Attacks

Model Context Protocol (MCP) enables tool-integrated LLM agents, but its third-party tool-server ecosystem expands software supply-chain risk across tool metadata, untrusted outputs, cross-tool flows, multi-modal inputs, and privileged sink actions. Existing MCP benchmarks mainly measure robustness to malicious inputs, offering limited support for dependency vetting, semantic metadata auditing, and hardening regression. We present MCP Pitfall Lab, a protocol-aware security testing framework that models developer pitfalls as reproducible scenarios and validates outcomes using MCP traces and objective validators rather than agent self-report. We also introduce Semantic MCP-Bill-of-Material(MCP-BOM), representing that augments component inventory with security-relevant tool semantics, including descriptions, schemas, high-risk parameters, source/sink roles, trust boundaries, policy hooks, audit support, and trace provenance. Across 2,579 validator-completed runs over four models, Pitfall Lab observes 31.9% overall attack success rate(ASR), with multi-modal injection strongest at 38.7%. Semantic static fields detect pitfalls involving policy-bearing tool descriptions, permissive schemas, missing audit support, and absent server-side validation with F1=0.727, while BOM-backed findings drop from 27 to 16 after hardening. Decomposed risk metrics show Control Coverage increasing from 0.173 to 0.697 and Residual Risk decreasing from 15.31 to 6.09. A trace-linked case study further demonstrates that cross-tool forwarding and image-to-tool leakage require runtime provenance rather than static manifest fields alone. Overall, Pitfall Lab reframes MCP tool servers as AI software-supply-chain dependencies and provides BOM-backed artifacts for review, hardening, and trace-grounded regression testing