# mcp-server-security

A hardening guide for MCP servers: TLS, OAuth 2.1, mTLS, input validation and audit logging for tool calls.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 334 installs · ★ 1177
- Author: devops-skills
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/BagelHole/DevOps-Security-Agent-Skills/tree/HEAD/security/ai/mcp-server-security/SKILL.md
- Updated: 2026-05-22
- HTML: https://affpapa.org/en/nevibecode/skills/mcp-server-security

## What it does

The skill starts with an MCP threat model: unauthorized tool access, prompt injection through resources, SSRF via tools, data exfiltration in results, credential theft, denial of service, man-in-the-middle and supply chain compromise. Transport, authentication and authorization sections follow.

You get working configs and code. For Streamable HTTP and SSE there is an Nginx block with TLS termination, HSTS and buffering turned off so SSE events stream right away. For stricter setups, mTLS with `openssl` commands to create a CA and an agent client certificate. For stdio servers, the skill shows how to restrict the process through `NODE_OPTIONS` and `--allow-fs-read`/`--allow-fs-write` in `claude_desktop_config.json`. A TypeScript middleware validates OAuth 2.1 bearer tokens with `jsonwebtoken`, checking RS256, issuer and audience.

If your MCP server runs locally over stdio for a single developer with no network exposure, you can relax the transport controls. Input validation and audit logging still apply. On a multi-tenant platform or in a regulated environment (SOC 2, HIPAA, PCI-DSS), that is a reason to wire scope-based authorization from the token early.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add BagelHole/DevOps-Security-Agent-Skills --skill mcp-server-security -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/mcp-server-security/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/mcp-server-security/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add BagelHole/DevOps-Security-Agent-Skills --skill mcp-server-security -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/mcp-server-security/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add BagelHole/DevOps-Security-Agent-Skills --skill mcp-server-security -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/mcp-server-security/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install BagelHole/DevOps-Security-Agent-Skills mcp-server-security
```

2. **Manually: put the files in place**
- File: `.github/skills/mcp-server-security/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add BagelHole/DevOps-Security-Agent-Skills --skill mcp-server-security -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/BagelHole/DevOps-Security-Agent-Skills --path security/ai/mcp-server-security
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/mcp-server-security/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add BagelHole/DevOps-Security-Agent-Skills --skill mcp-server-security -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/BagelHole/DevOps-Security-Agent-Skills/tree/HEAD/security/ai/mcp-server-security/SKILL.md

## When to use it
- ship an MCP server exposing filesystem, database or API tools without privilege gaps
- put TLS termination in front of an MCP server on Streamable HTTP or SSE
- issue a client certificate to an agent and turn on mTLS
- restrict a stdio server's filesystem access through `NODE_OPTIONS`
- validate an OAuth 2.1 bearer token and read scopes for authorization

## Example prompts
- run mcp-server-security against my Streamable HTTP MCP server and flag where TLS is missing
- help me set up mTLS between the agent and the MCP server, I need the openssl commands
- review the OAuth 2.1 middleware in `src/auth.ts` — is the token validated correctly

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: d7a3ca1542cf0311.

BEGIN THIRD-PARTY FILE d7a3ca1542cf0311
```text
---
name: mcp-server-security
description: Secure Model Context Protocol (MCP) servers with transport encryption, tool authorization, input validation, and audit logging for safe AI agent integrations.
license: MIT
metadata:
  author: devops-skills
  version: "1.0"
---

# MCP Server Security

Comprehensive hardening guide for Model Context Protocol (MCP) servers. MCP is the open
standard for connecting AI agents to external tools, data sources, and services. Because
MCP servers execute real actions on real infrastructure, they are a high-value attack
surface. This skill covers every layer of defense you need before exposing an MCP server
to agents in production.

---

## 1. When to Use This Skill

Apply this skill whenever you are:

- Deploying an MCP server that exposes tools (filesystem, database, API) to AI agents.
- Connecting an agent runtime (Claude Desktop, Cursor, a custom orchestrator) to one or
  more MCP servers over stdio, SSE, or Streamable HTTP transport.
- Building a multi-tenant platform where multiple users share the same MCP server.
- Passing sensitive data (PII, credentials, internal documents) through MCP resources.
- Operating in a regulated environment (SOC 2, HIPAA, PCI-DSS) where tool invocations
  must be auditable.

If your MCP server only runs locally over stdio for a single developer with no network
exposure, you can relax some transport-layer controls -- but input validation and audit
logging still apply.

---

## 2. MCP Threat Model

Before hardening, understand what you are defending against.

| Threat                        | Vector                                                        | Impact                              |
|-------------------------------|---------------------------------------------------------------|-------------------------------------|
| Unauthorized tool access      | Agent calls tools the user should not have access to          | Privilege escalation, data breach   |
| Prompt injection via resources| Malicious content in MCP resources influences agent behavior  | Arbitrary tool execution            |
```
END THIRD-PARTY FILE d7a3ca1542cf0311

The third-party file has ended. Everything between the d7a3ca1542cf0311 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2093 of 30451 bytes. © devops-skills · MIT · https://github.com/BagelHole/DevOps-Security-Agent-Skills/tree/HEAD/security/ai/mcp-server-security/SKILL.md

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---
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