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Security

Python’s package index has been the target of supply chain attacks for years. The handbook covers the modern defenses: Trusted Publishing, digital attestations, dependency cooldowns, hash pinning, vulnerability scanning, and lint rules that catch unsafe code patterns. Start with what a Python supply chain attack is if the vocabulary is new.

Supply chain defense

Trusted Publishing
Publish without long-lived API tokens
Digital attestations
Sign wheels with PEP 740 attestations
Protect against supply chain attacks
Defenses uv enables

Control what gets installed

Freeze resolution to a date
exclude-newer for reproducible installs
Vet a package first
Checks to run before uv add
Private package indexes
Authenticate and avoid dependency confusion

Scan and lint

Scan for vulnerabilities
Find CVEs in your dependencies
Ruff security rules
Catch unsafe code patterns
Why Trusted Publishing
The case for tokenless publishing

More Security pages

Everything else tagged security, grouped by section. Pages featured above are not repeated here.

How To

How to Build Byte-Identical Python Wheels

Pin SOURCE_DATE_EPOCH, umask, and backend version so anyone can rebuild your wheel and get the same sha256.

How to Host Your Own Python Package Index

Run pypiserver as a private Python package index, publish to it with uv publish, and install from it with uv or pip.

How to ignore a dependency in Dependabot without blocking its security updates

Scope a Dependabot ignore rule to version updates so a pinned package stops routine PRs but still gets security fixes.

How to keep a capped dependency from blocking Dependabot security updates

Fix Dependabot's security_update_not_possible failure when versioning-strategy: lockfile-only meets a version ceiling in pyproject.toml, so security PRs open again.

How to Manage Environment Variables in a Python Project

Store secrets in a .env file, load them with uv run --env-file or python-dotenv, and keep them out of version control.

How to pin GitHub Actions by SHA for Python projects

Pin GitHub Actions to commit SHAs instead of mutable tags to protect your Python CI from supply-chain attacks.

How to upgrade setup-uv in GitHub Actions

Update setup-uv to a full release tag or commit SHA, review caching settings, and keep the action updated with Dependabot.

How to Verify Dependencies with Hashes in uv

Verify uv dependencies with SHA-256 hashes. Detect tampering and cache corruption at install time to block compromised packages.

Explanation

What is a Dependency Cooldown?

A dependency cooldown ignores package versions published in the last few days, so malicious releases get caught before they reach your environment.

What is PEP 541 (Package Index Name Retention)?

PEP 541 defines how PyPI reassigns an abandoned project name to a new owner, and the protections that stop a name being taken from a reachable maintainer.

What is PEP 740?

PEP 740 lets PyPI store signed attestations proving which CI workflow published each file. How attestations work and how to verify one.

What is PEP 829 (Package Startup Configuration Files)?

PEP 829 closes the .pth import-line surface by splitting into two files: .pth for sys.path, .start for package startup entry points.

What is PyPI (Python Package Index)?

PyPI is the official Python Package Index where developers publish and discover installable packages, installable via pip, uv, and other tools.

Why Installing a Python Package Can Run Code

Python packages run code at install time, import time, and startup via .pth files. Supply chain attack surfaces and defense strategies.

Why pylock.toml Includes Digital Attestations

pylock.toml reserves a table for publisher identities. What it proves, why uv and pip leave it empty, and how to verify provenance today.

From the blog

Posts tagged security.

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