MCP Shield README

MCP Shield

Security scanner and MCP server for Model Context Protocol servers, tools, prompts, and AI agent projects.

MCP gives agents access to tools. MCP Shield helps you catch the obvious dangerous parts before they reach production: leaked secrets, shell execution, risky tool descriptions, prompt-injection text, and CI-breaking security regressions.

bash

mcp-scan .

text

[HIGH] code.shell_true server.py:42
  Shell execution is enabled.
  subprocess.run(cmd, shell=True)

[CRITICAL] secret.literal .env:1
  Possible hard-coded secret.
  OPENAI_API_KEY="sk-..."

Why MCP Shield

MCP servers often expose powerful capabilities: filesystem access, shell commands, network calls, credentials, browser automation, databases, and internal tools.

That is exactly where small mistakes become expensive:

a tool description encourages unsafe behavior
a test key becomes a real leaked token
an agent can call a shell command with user-controlled input
a prompt or resource contains injection text
CI has no security gate for MCP-specific risks

MCP Shield is the simple first line of defense: fast static checks, useful output, and a non-zero exit code when risk crosses your threshold.

Features

runs as both a CLI and an MCP server
built on the official MCP Python SDK
CI-friendly severity gates
text, JSON, Markdown, and SARIF output
inline suppressions with rule IDs
.mcp-scan-ignore for fixtures and intentional demos

What It Finds

Risk	Examples
Hard-coded secrets	API keys, tokens, passwords, private keys
Process execution	`subprocess`, `child_process`, `shell=True`
MCP tool risk	tools named or described as delete, shell, token, secret, filesystem
Environment access	`os.environ`, `process.env`
Prompt injection text	"ignore previous instructions", system prompt leakage phrases

Install

From a local checkout:

Terminal

pip install .

Run without installing:

bash

python -m mcp_security_scanner.cli .

MCP Server

Run MCP Shield as a stdio MCP server:

bash

mcp-shield-server

Available tools:

scan_path_tool - scan a local MCP server or agent project
list_rules - list rule IDs and descriptions

Example Claude Desktop-style command:

config.json

{
  "mcpServers": {
    "mcp-shield": {
      "command": "mcp-shield-server"
    }
  }
}

Usage

bash

mcp-scan .
mcp-scan path/to/mcp-server
mcp-scan . --format json
mcp-scan . --format markdown --output mcp-security-report.md
mcp-scan . --format sarif --output mcp-shield.sarif
mcp-scan . --fail-on medium

Formats:

text for humans
json for automation
markdown for PR comments and reports
sarif for GitHub code scanning

Severity gates:

low
medium
high
critical

--fail-on high exits with code 1 when any high or critical finding exists.

Ignore Files

Create .mcp-scan-ignore in the scanned directory:

gitignore

tests/
fixtures/
examples/unsafe-demo.py

Use this for intentional fixtures and demos. Do not use it to hide production risks.

Suppressions

Suppress a reviewed finding on the same line:

subprocess.run(cmd)  # mcp-shield: ignore code.subprocess

Use all only for test fixtures:

subprocess.run(cmd, shell=True)  # mcp-shield: ignore all

Example

Scan the intentionally unsafe example:

bash

python -m mcp_security_scanner.cli examples/unsafe-mcp-server --fail-on critical

GitHub Actions

yaml

name: MCP security scan

on: [push, pull_request]

jobs:
  scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: "3.12"
      - run: pip install .
      - run: mcp-scan . --fail-on high

Roadmap

MCP SDK-aware parsing for Python and TypeScript servers
safer default rule pack for enterprise MCP servers
prompt/resource-specific injection checks
PyPI release for pipx install mcp-shield

Repository Topics

Add these GitHub topics for discovery:

text

mcp, model-context-protocol, ai-agents, security, security-tools, scanner, devtools, llm, prompt-injection, static-analysis

GitHub recommends repository topics because they help people discover and contribute to projects by purpose and subject area.

Scope

MCP Shield is a static heuristic scanner. It catches common risks early, but it is not a full security audit.

Help It Grow

MCP security is moving fast. The most useful contributions right now are real-world unsafe MCP examples, low-noise detection rules, and CI integrations.

If MCP Shield catches something useful, star the repo so more MCP builders can find it.