Skill

Skill Subsonic-control636/agent-shield/skill

Scan AI agent skills, MCP servers, and plugins for security vulnerabilities. Use when: user asks to check a skill/plugin for safety, audit security, scan for backdoors/data exfiltration/credential leaks, or evaluate trust of a third-party skill. Triggers: "is this skill safe", "scan for security issues", "audit this plugin", "check for backdoors", "安全扫描", "扫一下安不安全".From its SKILL.md

Install

npx -y skills add Subsonic-control636/agent-shield --skill skill

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

3 things to look at

0 stars0 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.
runs commandsInstructs the agent to run 6 commands, including `npx @elliotllliu/agent-shield scan ./path/to/skill/` and 5 more.
fetches URLsInstructs the agent to fetch 1 URL, including https://github.com/user/repo.

SKILL.md

2.9 KB, 673 tokens by cl100k_base, as published. Nobody here has run it

AgentShield — Security Scanner

Scan any directory for security issues in AI agent skills, MCP servers, and plugins.

Usage

# Basic scan
npx @elliotllliu/agent-shield scan ./path/to/skill/

# Pre-install check (GitHub URL, npm package, or local path)
npx @elliotllliu/agent-shield install-check https://github.com/user/repo

# JSON output for programmatic use
npx @elliotllliu/agent-shield scan ./path/to/skill/ --json

# Fail if score is below threshold
npx @elliotllliu/agent-shield scan ./path/to/skill/ --fail-under 70

# Scan .difypkg plugin archives
npx @elliotllliu/agent-shield scan ./plugin.difypkg

What It Detects (30 rules)

High Risk:

data-exfil — reads sensitive files + sends HTTP requests
backdoor — eval(), exec(), dynamic code execution
reverse-shell — outbound socket to shell
crypto-mining — mining pool connections
credential-hardcode — hardcoded API keys/tokens
obfuscation — base64+eval, hex strings
prompt-injection — 55+ patterns, 12 categories, 8 languages
tool-shadowing — tool name/description manipulation
attack-chain — multi-step kill chain (5 stages)
cross-file — cross-file data flow and code injection
ast-* — Python AST taint tracking (eval, pickle, SQL injection, SSTI)
multilang-injection — 8-language prompt injection
description-integrity — semantic mismatch between description and code
mcp-runtime — MCP server runtime security issues

Medium Risk:

env-leak — process.env exfiltration
network-ssrf — user-controlled URLs, SSRF
privilege — SKILL.md permission vs code mismatch
supply-chain — known CVEs in dependencies
sensitive-read — SSH keys, AWS creds access
phone-home — periodic beacon/heartbeat pattern
python-security — 35 Python-specific patterns

Low Risk:

excessive-perms — too many permissions declared
hidden-files — .env with secrets committed
typosquatting — suspicious npm package names

Interpreting Results

Score 90-100: Low risk ✅
Score 70-89: Moderate risk — review warnings
Score 40-69: High risk — investigate before using
Score 0-39: Critical risk — do not install

When to Use

Before installing a third-party skill: npx @elliotllliu/agent-shield install-check <url>
Auditing your own skills before publishing
CI/CD pipeline gate: --fail-under 70
Reviewing skills from untrusted sources

What ships with it

Read from the repository

Just SKILL.md. No reference files, no scripts.