UI Drafter

Security
Getting rid of NPM scripts

by Eric Fortis

In 2016, Sam Saccone, from Google, discovered a vulnerability that allows adversaries to run arbitrary scripts when installing an NPM package of theirs. As mitigation, NPM co‑founder Laurie Voss suggests:

  • Option 1: using npm install --ignore-scripts
  • Option 2: adding ignore-scripts=true to .npmrc

I use the latter flag, so I don’t have to remember it. But for that, we will need something to replace NPM scripts. For example, a shell script or a Makefile.

Update 2021: Before NPM v7, enabling ignore‑scripts disabled NPM scripts. After v7, mentioned flag no longer disables them; it only prevents the life cycle scripts, which are the attack surface of the vulnerability.

Update 2022: Feross Aboukhadijeh, discovered a vulnerability when running NPM scripts. Therefore, we need an alternative again. Here are two:

Alternative 1: Shell script

#!/bin/sh

case $1 in
  dev)    ./make-dev.js ;;
  test)   mocha "src/**/*.test.js" ;;
  lint)   eslint src ;;
  slint)  stylelint "src/**/*.css" ;;

  prod)   time ./make-production.js ;;
  all)    $0 test && $0 lint && $0 slint && $0 prod ;;

  *)      echo "Invalid task $1" >&2; exit 1 ;;
esac

Which can be ran as:

$ ./run test

If the package is not globally installed, you can prefix the path:

lint) node_modules/.bin/eslint src ;;

Alternative 2: Makefile

As suggested in Hacker News, a Makefile:

dev:
	./make-dev.js
test:
	mocha "src/**/*.test.js"
lint:
	eslint src
slint:
	stylelint "src/**/*.css"

prod:
	sh -c "time ./make-production.js"

all: test lint slint prod

.PHONY: test lint slint prod all
$ make test

Overriding at installation

If you need packages that install binaries, or rely on running an NPM script, temporarily override the mitigation:

$ npm install --ignore-scripts=false package-i-trust

Or, trigger the installation script:

$ node node_modules/puppeteer/install.js 

Overriding a project

If you can’t follow the above recommendations for certain project, instead of allowing scripts globally, create an .npmrc file next to the package.json with the following line:

ignore-scripts=false

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