npm 12 Blocks Install Scripts by Default — Here's What Breaks and How to Prepare

Why Now: The Shai-Hulud Worm

The catalyst was unmistakable. On May 11, 2026, a threat group called TeamPCP released what researchers dubbed the "Mini Shai-Hulud" worm — the most sophisticated npm supply-chain attack on record. Without stealing a single credential, the attackers chained three GitHub Actions vulnerabilities to hijack TanStack's legitimate release pipeline and publish 84 malicious package versions across 42 packages.

Within six minutes, the worm had self-propagated. By end of day, over 170 packages on npm and PyPI were infected, including packages with 12+ million weekly downloads. The attack vector was painfully simple: postinstall scripts that ran automatically the moment a developer typed npm install.

The Three Breaking Changes

1. allowScripts defaults to OFF

npm install will no longer execute preinstall, install, or postinstall scripts from any dependency unless it has been explicitly approved. This includes:

• Native module builds triggered via node-gyp (packages with a binding.gyp are now blocked)
• prepare scripts from Git, local file, and linked dependencies

To manage your allowlist:

# See what would be blocked
npm approve-scripts --allow-scripts-pending

# Approve packages you trust
npm approve-scripts

# Explicitly block packages
npm deny-scripts

Results are written to package.json under allowScripts, pinned to installed versions (e.g., [email protected]: true). Commit this file so your whole team gets the same policy.

2. --allow-git defaults to none

npm install will no longer resolve Git dependencies (direct or transitive) unless explicitly permitted. This closes a code-execution path where a Git dependency's .npmrc could override which Git executable was used — bypassing --ignore-scripts entirely.

3. --allow-remote defaults to none

Dependencies from remote URLs (HTTPS tarballs, etc.) — both direct and transitive — are blocked unless permitted. The --allow-file and --allow-directory flags are not changing.

Package Manager Security Defaults: State of Play

Community Reaction

The developer community has largely welcomed the change. The most common reaction: "npm is the last major package manager to block install scripts by default — this is long overdue." pnpm's safer defaults have been one of its main selling points for years, and the TanStack incident demonstrated exactly why.

A minority of developers have noted the limitation: "Now all the malware can move from the install script to the module itself." This is true — npm 12 eliminates the most common automatic-execution attack vector, but it is not a full registry security guarantee. The goal is to close the most exploited path, not to solve supply-chain security entirely.