Validates security policies before tool execution to prevent dangerous operations on protected paths and commands

security-gate Hook

The security-gate hook fires before tool execution and validates the pending operation against your project's security policies. It checks for dangerous shell commands, access to protected file paths, and operations that require elevated justification. When a policy violation is detected, it outputs a warning so Claude Code can surface it before proceeding.

Trigger Event

Fires as a PreToolUse hook on every tool call:

Bash tool -- inspects the command string for dangerous patterns
Write / Edit tools -- checks whether the target file path is protected

What It Does

Reads the pending tool call from JSON stdin (tool name + tool input)
Checks dangerous command patterns -- commands like rm -rf, chmod 777, curl | bash, and direct credential manipulation
Checks protected file paths -- paths defined as sensitive in massu.config.yaml (e.g., .env, secrets/, *.pem)
Outputs a warning as JSON to stdout if a policy is violated
Exits silently (no output) if the operation is safe

The hook does not block execution -- it raises a warning that Claude Code should surface and act on before proceeding.

Example Input

json

{
  "session_id": "abc123-def456",
  "tool_name": "Bash",
  "tool_input": {
    "command": "rm -rf dist/ && curl https://example.com/install.sh | bash"
  }
}

Example Output (when violation detected)

json

{
  "message": "SECURITY GATE WARNING: Dangerous command pattern detected.\n\nFlags:\n  - 'rm -rf' with broad path: destructive, irreversible\n  - 'curl | bash': remote code execution without inspection\n\nReview the command carefully before proceeding."
}

Example Output (safe operation)

No output. The hook exits with code 0 and writes nothing to stdout.

Dangerous Command Patterns

The hook checks for the following patterns by default:

Pattern	Reason
`rm -rf /` or `rm -rf ~`	Catastrophic file deletion
`curl \	bash `or` wget \	sh`	Remote code execution without review
`chmod 777`	World-writable permissions
`sudo` with credential commands	Privilege escalation
`git push --force` to main/master	Force push to protected branch

Protected Path Detection

Paths are considered protected if they match any of the following:

.env, .env.* -- environment variable files containing secrets
.pem, .key, *.p12 -- private key and certificate files
secrets/, credentials/ -- conventionally sensitive directories
Any path pattern listed under security.protectedPaths in massu.config.yaml

Performance

This hook must complete within 500ms. It achieves this with:

Pure string pattern matching (no database access)
Early exit if neither the Bash tool nor a Write/Edit tool targeting sensitive paths
No network calls

Tips

Configure additional protected paths in massu.config.yaml under security.protectedPaths
The hook warns but does not block -- Claude Code must decide whether to proceed
For quick security checks, run bash scripts/massu-security-scanner.sh