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claude-skill-antivirus

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Security scanner for Claude Code Skills — 9 engines detect malicious patterns, data exfiltration, dangerous ops across 71K+ skills

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# Claude Skill Antivirus

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<img src="assets/demo.gif" alt="Claude Skill Antivirus scanning a CLAUDE.md file for prompt injection" title="Demo shows: trigger scan → detect patterns → show results" />

A security scanner and safe installer for Claude Code Skills. Detects malicious patterns, data exfiltration attempts, and dangerous operations before installing third-party skills.

Compatible with Claude Code using Opus 4.6, Sonnet 4.6, and Haiku 4.5 models.

[繁體中文說明](./README.zh-TW.md) | [SkillsMP Scan Report](./SCAN-REPORT.md)

## SkillsMP Platform Scan Results

We scanned all **71,577 skills** on SkillsMP:

| Risk Level | Count | Percentage |
|------------|-------|------------|
| CRITICAL | 91 | 0.13% |
| HIGH | 626 | 0.87% |
| MEDIUM | 1,310 | 1.83% |
| SAFE | **69,505** | **97.11%** |

**~3% of skills may have potential risks.** See [full report](./SCAN-REPORT.md) for details.

> **Note**: Some findings may be false positives (e.g., legitimate 1Password/Bitwarden integrations). Manual review is recommended for flagged skills.

## Features

- **9 Security Scanning Engines**:
  - Dangerous Commands Scanner - Detects destructive shell commands
  - Data Exfiltration Scanner - Identifies data theft patterns
  - External Connections Scanner - Analyzes URLs and network calls
  - Permission Scanner - Reviews tool permissions and access scope
  - Pattern Scanner - Detects prompt injection and sensitive data
  - MCP Security Scanner - Validates MCP server configurations
  - SSRF Scanner - Identifies server-side request forgery patterns
  - Dependency Scanner - Detects malicious packages and typosquatting
  - Sub-agent Scanner - Detects Task tool abuse and agent chain attacks

- **Risk Assessment**: Critical, High, Medium, Low, and Info levels
- **Multilingual Support**: English and Traditional Chinese (繁體中文)
- **Install or Scan-Only Mode**: Review skills before installation
- **Interactive Prompts**: Guided decision-making for risky installations

## Installation

```bash
npm install -g claude-skill-antivirus
```

Or run directly with npx:

```bash
npx claude-skill-antivirus <skill-source>
```

## Usage

### Install a skill with security scanning

```bash
# Install to project level (./.claude/skills/) - default
skill-install ./path/to/skill
skill-install https://github.com/user/skill-repo

# Install to user level (~/.claude/skills/)
skill-install ./path/to/skill --global
skill-install @skillsmp/example-skill -g
```

**Installation paths:**
- Project level (default): `./.claude/skills/`
- User level (`--global`): `~/.claude/skills/`

### Scan only (without installing)

```bash
skill-install ./path/to/skill --scan-only
```

### Change language

```bash
# English (default)
skill-install ./path/to/skill --lang en

# Traditional Chinese
skill-install ./path/to/skill --lang zh-TW
```

### Alternative command

```bash
claude-skill-av ./path/to/skill --scan-only
```

### Batch scan all SkillsMP skills

```bash
# Scan all skills from SkillsMP (requires API key)
skill-batch-scan --api-key <your-api-key>

# Scan with options
skill-batch-scan --api-key <key> --max-pages 10 --verbose
skill-batch-scan --api-key <key> --output ./my-reports --lang zh-TW
```

Options:
- `-k, --api-key <key>` - SkillsMP API key (required)
- `-l, --limit <number>` - Skills per page (default: 100)
- `-p, --max-pages <number>` - Maximum pages to scan (default: all)
- `-o, --output <dir>` - Output directory for reports (default: ./scan-reports)
- `-v, --verbose` - Show verbose output
- `--lang <lang>` - Language (en, zh-TW)

## Scanning Engines

### 1. Dangerous Commands Scanner

Detects commands that can cause system damage:

| Risk Level | Detection Items |
|------------|-----------------|
| Critical | `rm -rf /`, `curl \| bash`, fork bombs |
| High | Reading `/etc/shadow`, reverse shells, credential theft |
| Medium | `rm -rf`, permission changes, service control |
| Low | `sudo`, global package installs |

### 2. Permission Scanner

Analyzes `allowed-tools` declarations:

- **Critical**: `Bash(*)` - Unrestricted shell access
- **High**: `Write`, `WebFetch`, broad bash permissions
- **Medium**: `Read`, `Glob`, `Grep`, version control tools
- **Dangerous Combinations**: e.g., `Read + WebFetch` = data exfiltration risk

### 3. External Connections Scanner

Identifies suspicious network activity:

- Direct IP URLs
- Webhook/data capture services
- Suspicious TLDs (.tk, .ml, etc.)
- Discord/Telegram webhooks
- URL shortening services

### 4. Pattern Scanner

Detects:

- Prompt injection attacks
- Hardcoded credentials/API keys
- Obfuscated code (base64, hex encoding)
- Social engineering language

### 5. Data Exfiltration Scanner

Specifically detects malicious behavior of reading local data and sending it externally:

| Category | Detection Items |
|----------|-----------------|
| Data Collection | Reading `.ssh`, `.aws`, `.env`, browser passwords, password managers |
| Data Exfiltration | `curl -d`, netcat transfers, DNS tunneling, email exfiltration |
| Combined Attacks | `cat \| base64 \| curl`, `tar \| nc`, `find -exec curl` |
| Env Variable Theft | `env \| curl`, `printenv` exfiltration |
| System Recon | `whoami`, `hostname`, network config exfiltration |
| Persistence | Modifying `.bashrc`, scheduled cron exfiltration |

### 6. MCP Security Scanner

Detects security risks in MCP Server configurations:

| Category | Detection Items |
|----------|-----------------|
| Untrusted Sources | Non-official MCP servers, direct URL execution |
| Dangerous Permissions | Unrestricted filesystem access, shell execution, database access |
| Sensitive Config | Environment variables with credentials, exposed config |
| Dangerous Combinations | Filesystem + Fetch, Shell + Network |

### 7. SSRF Scanner

Detects Server-Side Request Forgery and cloud attacks:

| Category | Detection Items |
|----------|-----------------|
| Cloud Metadata | AWS/GCP/Azure 169.254.169.254, IAM credential theft |
| Internal Network | 10.x.x.x, 192.168.x.x, 172.16-31.x.x probing |
| SSRF Bypass | Hex IP, URL encoding, file://, gopher:// |
| Kubernetes | API access, secrets theft, serviceaccount |
| Docker | docker.sock access, privileged containers, container escape |

### 8. Dependency Scanner

Detects malicious or vulnerable dependencies:

| Category | Detection Items |
|----------|-----------------|
| Known Malicious | event-stream, ua-parser-js, colors, faker |
| Typosquatting | crossenv, lodash-, mongose, reqeusts |
| Suspicious Install | URL installs, insecure registry, HTTP index |
| postinstall Risks | Install scripts with curl, wget, eval |

### 9. Sub-agent Scanner

Detects Task tool and sub-agent abuse:

| Category | Detection Items |
|----------|-----------------|
| Privilege Escalation | Task spawning Bash agent, requesting all permissions |
| Prompt Injection | Sub-agent prompts with malicious commands |
| Agent Chain Attacks | Nested Task calls, recursive agents |
| DoS Attacks | Loop Task calls, infinite recursion |
| Data Theft | Read + WebFetch combinations, accessing sensitive data |

## Output Examples

### Safe Skill

```
🔧 Claude Skill Installer v2.0.0

📦 Skill loaded: example-safe-skill

🔍 Starting security scan...

===========================================
     SECURITY SCAN REPORT
===========================================
Risk Level: ✅ SAFE

📊 Findings Summary:
  🟢 CRITICAL: 0
  🟢 HIGH:     0
  🟢 MEDIUM:   0
  🟢 LOW:      0
  ℹ️  INFO:     2

✅ Recommendation: Safe to install
```

### Malicious Skill Detected

```
🔧 Claude Skill Installer v2.0.0

📦 Skill loaded: suspicious-skill

🔍 Starting security scan...

===========================================
     SECURITY SCAN REPORT
===========================================
Risk Level: ☠️ CRITICAL

📊 Findings Summary:
  🔴 CRITICAL: 5
  🟠 HIGH:     3
  🟡 MEDIUM:   2
  🟢 LOW:      1
  ℹ️  INFO:     4

🔴 CRITICAL Findings:
  • [Data Collection] Reading sensitive credential files
    Attempts to read environment variables, private keys or credential files
  • [Data Exfiltration] curl sending command output
    Using curl to send command execution results to external server
  ...

❌ Recommendation: DO NOT INSTALL - Contains critical security risks
```

## Risk Levels

| Level | Score Impact | Action |
|-------|--------------|--------|
| CRITICAL | -30/item | Block installation |
| HIGH | -20/item | Require explicit confirmation |
| MEDIUM | -10/item | Show warning |
| LOW | -5/item | Show in verbose mode |
| INFO | 0 | Always show |

## API

You can also use the scanner programmatically:

```javascript
import { SecurityScanner, loadSkill } from 'claude-skill-antivirus';

const scanner = new SecurityScanner();
const skill = await loadSkill('./path/to/skill');
const findings = await scanner.scan(skill);

console.log(findings);
// {
//   critical: [...],
//   high: [...],
//   medium: [...],
//   low: [...],
//   info: [...]
// }
```

## Project Structure

```
claude-skill-antivirus/
├── src/
│   ├── index.js                   # CLI entry point
│   ├── i18n/                      # Internationalization
│   │   ├── index.js
│   │   ├── en.js                  # English translations
│   │   └── zh-TW.js               # Traditional Chinese translations
│   ├── scanner/
│   │   ├── index.js               # Main scanner (integrates 9 engines)
│   │   ├── dangerous-commands.js  # Dangerous command detection
│   │   ├── permissions.js         # Permission checking
│   │   ├── external-connections.js # External connection analysis
│   │   ├── patterns.js            # Pattern matching
│   │   ├── data-exfiltration.js   # Data exfiltration detection
│   │   ├── mcp-security.js        # MCP Server security check
│   │   ├── ssrf-scanner.js        # SSRF/cloud attack detection
│   │   ├── dependency-scanner.js  # Dependency security check
│   │   └── subagent-scanner.js    # Sub-agent attack detection
│   └── utils/
│       ├── downloader.js          # Skill downloader
│       └── installer.js           # Skill installer
├── examples/
│   ├── safe-skill/                # Safe example
│   └── malicious-skill/           # Malicious example (tests all engines)
├── package.json
└── README.md
```

## Latest Updates

### v2.1.0 (2026-03-13)
- Verified compatibility with Claude Code Opus 4.6
- Updated documentation and metadata

### v2.0.1
- Separated capability warnings from actual threats in permission scanner
- Fixed array format handling in `allowed-tools`

### v2.0.0
- Added 4 new scanning engines: MCP Security, SSRF, Dependency, and Sub-agent scanners (total: 9 engines)
- Added i18n support (English + Traditional Chinese)
- Added batch scanner for SkillsMP platform
- Scanned all 71,577 skills on SkillsMP

### v1.0.0
- Initial release with 5 core scanning engines
- CLI installer with interactive prompts

## Related Projects

- [cf-browser](https://github.com/claude-world/cf-browser) - Open-source Cloudflare Browser Rendering proxy with 9 MCP tools for Claude Code
- [claude-world.com](https://claude-world.com) - Claude Code advanced usage community

## Contributing

Contributions are welcome! Please feel free to submit issues and pull requests.

### Adding New Detection Patterns

Each scanner is modular. To add new patterns:

1. Find the appropriate scanner in `src/scanner/`
2. Add your pattern to the relevant array
3. Include: `pattern`, `risk`, `title`, `description`

## License

MIT

## Author

Lucas Wang <support@claude-world.com>

## Links

- [GitHub Repository](https://github.com/claude-world/claude-skill-antivirus)
- [npm Package](https://www.npmjs.com/package/claude-skill-antivirus)
- [Report Issues](https://github.com/claude-world/claude-skill-antivirus/issues)

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