DEV Community

Cover image for I Almost Installed a Malicious Python Package: So, I Built trustcheck
Halfblood Prince
Halfblood Prince

Posted on

I Almost Installed a Malicious Python Package: So, I Built trustcheck

#python #security #opensource #devtool

A few months ago, I was doing something completely normal. I needed a small Python library. So, I did what every Python developer does:

pip install <package>
Enter fullscreen mode Exit fullscreen mode

But before hitting enter I paused. Something felt off. The package name looked right... but also slightly wrong. And that moment made me realize something uncomfortable:

We trust PyPI packages far more than we should.

That realization led me to build trustcheck --- a tool that helps developers verify the trustworthiness of PyPI packages before installing them.

The uncomfortable truth about pip install

Installing dependencies is the most normal thing in software
development. But under the hood we are doing something pretty risky:

pip install something-from-the-internet
Enter fullscreen mode Exit fullscreen mode

In many cases we don't check:

  • who published the package
  • whether the artifact matches the source repo
  • whether the maintainer account was compromised
  • whether the package name is a typo
  • whether the release came from a trusted build system

And attackers know this.

Attack #1: The typo that steals your secrets

One of the simplest attacks is typosquatting. An attacker uploads a package with a name that looks almost identical to
a popular one.

Example:

Real package Malicious typo
requests reqeusts
urllib3 urlib3
tensorflow tensorlfow

Developers type quickly. CI scripts copy‑paste dependencies. And suddenly a malicious package gets installed.

Real malicious PyPI packages have been caught doing things like:

  • exfiltrating AWS credentials
  • stealing SSH keys
  • sending environment variables to remote servers

All triggered by a simple:

pip install reqeusts
Enter fullscreen mode Exit fullscreen mode

Attack #2: Dependency confusion

This one is even sneakier.

Imagine a company has an internal package called:

internal-utils
Enter fullscreen mode Exit fullscreen mode

An attacker uploads a public PyPI package with the same name. Then they give it a higher version number. If a developer runs:

pip install internal-utils
Enter fullscreen mode Exit fullscreen mode

pip might install the malicious public package instead of the internal
one. This technique was used in large-scale research that successfully
injected packages into major companies.

Attack #3: The compromised maintainer

Sometimes the attack doesn't involve fake packages at all. Instead, the real maintainer account gets compromised. Then the attacker publishes a new version like:

package 2.4.1
Enter fullscreen mode Exit fullscreen mode

Everything looks legitimate. Same project. Same PyPI page.
But the new release contains malicious code. This has happened multiple times across open-source ecosystems.

The problem: we rarely verify packages

The ecosystem is built on trust. But trust without verification is fragile.

Developers typically check:

  • GitHub stars
  • number of downloads
  • README quality

But those signals do not guarantee that a specific release artifact is
trustworthy. That's the gap trustcheck tries to fill.

Introducing trustcheck

trustcheck is a Python CLI that evaluates the trust signals of PyPI
releases before installation. Instead of blindly installing a package, you can inspect it first. It analyzes signals like:

  • PyPI release metadata
  • provenance information
  • Trusted Publisher hints
  • repository links
  • publisher consistency
  • vulnerability records

The goal is simple:

Turn blind trust into evidence‑based trust.

Installation 

pip install trustcheck
Enter fullscreen mode Exit fullscreen mode

Basic usage

Check the trust signals for a package:

trustcheck inspect requests
Enter fullscreen mode Exit fullscreen mode

Check a specific version:

trustcheck inspect sampleproject --version 4.0.0
Enter fullscreen mode Exit fullscreen mode

Check dependencies too:

trustcheck inspect sampleproject --version 4.0.0 --with-deps
Enter fullscreen mode Exit fullscreen mode

Or inspect the full dependency tree:

trustcheck inspect sampleproject --version 4.0.0 --with-transitive-deps
Enter fullscreen mode Exit fullscreen mode

Enforcing repository expectations

You can also verify that a package actually comes from the repository
you expect.

trustcheck inspect sampleproject \
  --version 4.0.0 \
  --expected-repo https://github.com/pypa/sampleproject
Enter fullscreen mode Exit fullscreen mode

If something doesn't match, trustcheck flags it.

This helps defend against:

  • dependency confusion
  • publisher drift
  • repository mismatches

CI integration

trustcheck can output JSON for automation:

trustcheck inspect sampleproject --version 4.0.0 --format json
Enter fullscreen mode Exit fullscreen mode

This makes it easy to integrate into:

  • CI pipelines
  • dependency review bots
  • internal security tooling

A better dependency workflow

Instead of:

pip install random-package
Enter fullscreen mode Exit fullscreen mode

A safer workflow looks like:

1️⃣ Inspect package trust with trustcheck
2️⃣ Install dependency
3️⃣ Scan for vulnerabilities with pip-audit

Small change. Much safer ecosystem.

Why this matters

Modern applications depend on hundreds of packages. A single malicious dependency can:

  • leak secrets
  • compromise builds
  • inject backdoors
  • affect thousands of downstream users

Supply chain security is becoming one of the most important areas in
software development. trustcheck is a small step toward bringing those ideas into everyday Python workflows.

Try it out

GitHub: https://github.com/Halfblood-Prince/trustcheck
PyPI: https://pypi.org/project/trustcheck/

Top comments (0)

The discussion has been locked. New comments can't be added.