PDM Trojan Lockfile

Summary

It’s possible to craft a malicious pdm.lock file that could allow e.g. an insider or a malicious open source project to appear to depend on a trusted PyPI project, but actually install another project.

Details

Project foo can be targeted by creating the project foo-2 and uploading the file foo-2-2.tar.gz to pypi.org. PyPI will see this as project foo-2 version 2, while PDM will see this as project foo version 2-2. The version must only be parseable as a version (and the filename must be a prefix of the project name), but it’s not verified to match the version being installed. (Version 2-2 is also not a valid normalized version per PEP 440.)

Matching the project name exactly (not just prefix) would fix the issue. The version should also be verified to avoid version downgrade attacks.

PoC

Example pdm.lock snippet to appear to depend on foo but actually install foo-2

"foo 2.2.0" = [
  url = "https://files.pythonhosted.org/.../foo-2-2.tar.gz
]

Impact

When installing dependencies with PDM, what’s actually installed could differ from what’s listed in pyproject.toml (including arbitrary code execution on install). It could also be used for downgrade attacks by only changing the version.