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MCP Security Analysis

Executive Summary

This document provides an in-depth security analysis of the Model Context Protocol (MCP), reflecting the specification schema version 2025-03-26, examining its core components, communication patterns, and trust boundaries based on the specification and reference implementations. The analysis aims to identify potential vulnerabilities and guide the secure development and deployment of MCP-based applications.

MCP facilitates powerful integrations but introduces significant security considerations that must be addressed by implementers (Hosts, Clients, Servers), as the protocol itself cannot enforce many security guarantees. Key high-risk areas include:

  1. Tool Execution (tools/call): Represents a direct arbitrary code execution risk requiring rigorous server-side input validation, authorization, output sanitization, and strong client-side user confirmation.
  2. User Consent & Control: The specification mandates, and secure implementation demands, explicit, informed user consent mediated by the Host/Client for actions like tool execution, sampling requests, and resource access. Failure here undermines the entire security model.
  3. Resource Access (resources/read, etc.): Requires meticulous server-side URI validation (preventing path traversal) and strict access control checks before serving resource data.
  4. Input Validation: Both Clients and Servers must rigorously validate all incoming parameters to prevent various injection attacks and denial-of-service.
  5. Sampling (sampling/createMessage): Exposes risks of prompt injection against the client's LLM and potential resource abuse (cost, rate limits) if not carefully controlled by the client with user oversight.

Secure implementation requires adherence to principles like least privilege, defense-in-depth, secure defaults, transport security (HTTPS/WSS), robust authentication/authorization (e.g., OAuth 2.1/PKCE), careful data handling to prevent leakage (especially in logs and errors), and secure interaction with external systems. This analysis provides detailed recommendations and identifies specific control points across the protocol's features and trust boundaries.

1. Introduction

This document provides a detailed analysis of the Model Context Protocol (MCP) focusing on its interactions, message types, data fields, potential extension points, data flows, trust boundaries, and communication patterns. The primary goal is to identify potential security considerations and attack surfaces within the MCP ecosystem to inform the development of the mcp-security project.

Analysis is based on the 2025-03-26 version of the MCP specification (documented at modelcontextprotocol.io and defined in the modelcontextprotocol/specification repository) and insights from the reference implementations in the modelcontextprotocol/servers repository (covering TypeScript examples and the Python SDK).