🛡️ Security Guard MCP

Security Guard MCP is an enterprise-grade security gateway designed specifically for the Model Context Protocol (MCP). It acts as a zero-trust intermediary between Large Language Models (LLMs) and MCP tools, ensuring that every interaction is audited, sanitized, and compliant with corporate security policies.

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🌟 Overview

As LLMs gain the ability to execute tools and access local/remote contexts via MCP, the risk of accidental data leakage or unauthorized system access increases. Security Guard MCP provides a robust defense layer that:

• Prevents Exfiltration: Automatically masks sensitive data (API keys, tokens, passwords) from tool outputs.
• Enforces Least Privilege: Implements RBAC and granular policy control over tool execution.
• Secures the File System: Blocks access to sensitive system files and configuration directories.
• Ensures Accountability: Logs every tool call and context exchange for audit and compliance.

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🤖 For AI Agent Developers

If you are building AI Agents (using LangChain, AutoGPT, or custom MCP clients), Security Guard MCP solves the "Trust Gap" between your agent and your infrastructure.

Why use this?

When you give an AI Agent a tool (e.g., "Read File" or "Execute SQL"), you are essentially giving it a "shell" into your environment. Security Guard MCP ensures:

• Prompt Injection Defense: Filters malicious intent before it reaches your sensitive tools.
• Context Isolation: Limits what the agent can "see" and "touch" based on strictly defined scopes.
• Safe Experimentation: Developers can test autonomous agents without worrying about them accidentally deleting data or leaking .env files.

🔄 The Security Flow

graph LR
    subgraph "Untrusted Zone"
        A[AI Agent / LLM]
    end

    subgraph "Security Guard MCP (Safe Zone)"
        B{Gateway}
        C[Policy Engine]
        D[Sanitizer]
        E[Audit Log]
    end

    subgraph "Internal Infrastructure"
        F[File System]
        G[Database]
        H[Internal APIs]
    end

    A -- "MCP Request" --> B
    B -- "Check RBAC" --> C
    C -- "Allowed" --> F & G & H
    F & G & H -- "Raw Output" --> D
    D -- "Masked Output" --> B
    B -- "Secure Context" --> A
    B -- "Async Event" --> E

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🏗️ Architecture

Built on a modular NestJS Monorepo architecture, the project is divided into specialized micro-services and libraries:

Applications

• Gateway (apps/gateway): The main entry point. Handles incoming MCP requests, performs authentication, and dispatches tasks through the security pipeline.

Core Libraries

• libs/sanitizer: Deep-content inspection engine for auto-masking sensitive strings.
• libs/scanner: Security scanner for file path validation and protocol-level threat detection.
• libs/policy: Policy engine for RBAC and dynamic tool-access rules.
• libs/auth: Unified authentication layer.
• libs/audit: High-performance audit logging via Kafka.

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🛡️ Security Controls

1. Auto-Masking (DLP)

The system automatically detects and masks sensitive keys in JSON payloads and tool responses, including:

• password, secret, token, apikey, privateKey, clientSecret.

2. File System Protection

Protects the host environment by blocking access to:

• Configurations: .env*, application-prod.yml, terraform.tfvars
• Credentials: *.pem, *.key, id_rsa, known_hosts, secrets/*
• Certificates: *.p12, *.jks

3. Enterprise Features

• Audit Logging: Asynchronous logging to Kafka for long-term retention and SIEM integration.
• Observability: Native OpenTelemetry support for distributed tracing and Prometheus metrics.
• High Performance: Built on Fastify for ultra-low latency security overhead.

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🛠️ Tech Stack

• Framework: NestJS + Fastify
• Protocol: Model Context Protocol SDK
• Database: PostgreSQL with Prisma ORM
• Caching: Redis (ioredis)
• Messaging: Apache Kafka (kafkajs)
• Validation: Zod

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🚀 Getting Started

Prerequisites

• Node.js v20+
• Docker & Docker Compose
• A running MCP-compatible Client (e.g., Claude Desktop, Gemini CLI)

Installation

1. Clone the repository:

   git clone https://github.com/your-org/security-guard-mcp.git
   cd security-guard-mcp
   

2. Install dependencies:

   npm install
   

3. Environment Setup:

   cp .env.example .env
   # Update .env with your local database and Kafka credentials
   

4. Spin up Infrastructure:

   docker compose up -d
   

5. Run the Application:

   # Development mode
   npm run start:dev
   
   # Production build
   npm run build
   npm run start:prod
   

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📄 License

This project is licensed under the MIT License - see the LICENSE file for details.