attach-dev

attach-guard

Supply chain security plugin for Claude Code. Blocks compromised packages before they're installed.

The Problem

Claude Code installs packages on your behalf — often without you reviewing each one. Existing security tools scan after the fact or rely on advisory prompts that Claude can skip. There is no open-source guardrail that sits directly in front of package install commands and blocks risky packages before they execute.

What attach-guard Does

attach-guard is a Claude Code plugin that intercepts package installation commands and evaluates them against policy before execution. It is not an advisory scanner. It is a hard enforcement boundary.

• Installs as a Claude Code plugin — no manual hook configuration needed
• Intercepts npm install, pnpm add, pip install, go get, and cargo add commands via PreToolUse hooks
• Checks package scores, age, and alerts via Socket.dev
• Denies known malware and low-score packages automatically
• Asks for confirmation on gray-band packages
• Rewrites unpinned installs to safe pinned versions when possible
• Fails closed when the provider is unavailable
• Logs every decision to a local JSONL audit trail

Smart Version Replacement: Block Without Breaking Flow

Most security tools just say "no." attach-guard says "no, but here's a safe alternative."

When a risky version is blocked, attach-guard finds the newest version that passes policy and offers it as a replacement. Claude sees the safe alternative and can proceed immediately — your flow doesn't stop, it gets redirected to a safe path.

npm — axios v1.14.1 and v0.30.4 were compromised versions published via a hijacked maintainer account:

> npm install axios

attach-guard evaluates:
  axios@1.14.1  -->  DENY (supply chain score 40, below threshold 50 — compromised version)
  axios@1.14.0  -->  ALLOW (supply chain score 71, passes all policy checks)

Result: ASK + rewritten command
  "npm install axios@1.14.0"

pip — litellm v1.82.7 and v1.82.8 were malicious versions published to PyPI:

> pip install litellm

attach-guard evaluates:
  litellm==1.82.8  -->  DENY (compromised version)
  litellm==1.82.6  -->  ALLOW (passes all policy checks)

Result: ASK + rewritten command
  "pip install litellm==1.82.6"

These are real examples — attach-guard blocks compromised versions automatically based on their supply chain scores.

Scenario	Example	Decision	What happens
Package is safe	npm install axios@1.14.0	Allow	Install proceeds normally
Pinned to compromised version	pip install litellm==1.82.8	Deny	Blocked — compromised version
Unpinned, latest is risky	npm install axios	Ask + rewrite	Safe alternative offered: axios@1.14.0
All versions fail	malware-only package	Deny	Blocked with clear explanation

This works across all supported ecosystems — the rewrite uses the native pinning syntax for each:

Ecosystem	Unpinned command	Rewritten command
npm / pnpm	npm install axios	npm install axios@1.14.0
pip	pip install litellm	pip install litellm==1.82.6
Go	go get golang.org/x/net	go get golang.org/x/net@v0.25.0
Cargo	cargo add serde	cargo add serde@=1.0.200

Your flow only fully stops when there is genuinely no safe version to offer.

Why a Hook, Not a Skill or MCP

attach-guard uses Claude Code hooks — not skills or MCP servers. The distinction matters:

• Hooks run automatically on every matching tool call. They enforce rules deterministically — Claude cannot skip or override them.
• Skills are instructions Claude follows when invoked. They guide behavior but cannot block actions.
• MCP servers provide advisory context. They inform but do not enforce.

Security enforcement requires interception at the tool-call boundary, before execution. Hooks are the only Claude Code extension point that guarantees this.

Installation

Quick Start: Claude Code Plugin

The fastest way to try attach-guard. Requires a Socket.dev API token (free tier available).

# Add the marketplace and install (one-time)
claude plugin marketplace add attach-dev/attach-guard
claude plugin install attach-guard@attach-dev

Or from within a Claude Code session:

/plugin marketplace add attach-dev/attach-guard
/plugin install attach-guard@attach-dev

During installation or enablement, Claude Code will prompt for your Socket API token (stored securely in your system keychain). Get a free token at socket.dev.