trace-npm

See what an npm lifecycle script actually did: files touched, processes spawned, network endpoints contacted.

What did this package script actually do on my machine?

It is Linux-first and intentionally small. It runs a package script under strace and emits a readable report.

npx trace-npm run --package some-package --script postinstall --i-understand-this-executes-untrusted-code

For development or CI fixtures, parse a saved trace anywhere:

npx trace-npm report --trace-file ./postinstall.strace --package some-package --script postinstall

What It Reports

• files read or written
• child programs executed
• network endpoints contacted
• suspicious paths such as ~/.ssh, ~/.aws, .env, shell profiles, and keychains
• JSON output for CI or later policy tooling
• visible trace-loss accounting
• a limitations block in every report

Non-Goals

• Not a sandbox.
• Not a malware verdict engine.
• Not a package reputation score.
• Not a replacement for npm approval.
• Not cross-platform in v0.

The goal is evidence, not vibes.

Suggested Workflow

run executes the target lifecycle script. That is unsafe for genuinely untrusted packages. The current host runner uses a synthetic HOME, timeout, and explicit danger flag, but it is not a sandbox. A disposable container runner is required before this should be treated as a safer detonation workflow.

Canary Credentials

When trace-npm run executes a script, it provides a synthetic HOME directory. To catch scripts that silently check for the existence of high-value targets before deciding to steal them (conditional exfiltration), trace-npm populates this HOME with inert, fake credentials:

• ~/.ssh/id_rsa
• ~/.npmrc
• ~/.aws/credentials

These tokens are marked CANARY and are unusable. If a script attempts to read them, it will trip the canary and leave undeniable proof of malicious intent in the trace report.

Running on macOS / Windows (Docker)

trace-npm run requires Linux and strace. If you are on macOS or Windows, you can safely run it using this Docker one-liner from the root of your project:

docker run -it --rm -v "$PWD":/w -w /w ubuntu:24.04 bash -c \
  "apt-get update -qq && apt-get install -y -qq strace nodejs npm && npm install --ignore-scripts && npx trace-npm run --package <target-package> --script postinstall --i-understand-this-executes-untrusted-code"

Install dependencies with scripts disabled, then inspect lifecycle scripts before approving them.

npm install --ignore-scripts
npx trace-npm run --package some-package --script postinstall --i-understand-this-executes-untrusted-code

Exit Codes

0  clean report or --fail-on none
1  tool error
2  suspicious findings or selected fail-on condition present

Current Status

This is a first prototype:

• run requires Linux and strace.
• report works on any platform from a saved strace log.
• package attribution is currently script-level, not individual nested package-level.
• network reporting is endpoint-level, not DNS-name-level.
• non-blocking connection outcomes are reported as pending unless final status can be determined from traced syscalls.
• file contents are not captured.
• a clean report is not proof that a package is safe.
• host run is not a sandbox.
• macOS live tracing is not supported in v0.

Development

npm test
npm run check
node ./bin/trace-npm.js report --trace-file ./test/fixtures/postinstall.strace --package suspect --script postinstall