Agent Shield

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

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