PyPI Python Package Repository Patches Critical Supply Chain Flaw

The maintainers of Python Package Index (PyPI) last week issued
fixes for three vulnerabilities, one among which could be abused to
achieve arbitrary code execution and take full control of the
official third-party software repository.

The security weaknesses were discovered^[1]
and reported by Japanese security researcher RyotaK, who in the
past has disclosed critical vulnerabilities in the Homebrew Cask repository^[2] and Cloudflare’s
CDNJS library^[3]. He was awarded a total
of $3,000 as part of the bug bounty program.

The list of three vulnerabilities is as follows –

• Vulnerability in Legacy Document Deletion on
  PyPI^[4] – An exploitable
  vulnerability in the mechanisms for deleting legacy documentation
  hosting deployment tooling on PyPI, which would allow an attacker
  to remove documentation for projects not under their control.
• Vulnerability in Role Deletion on
  PyPI^[5] – An exploitable
  vulnerability in the mechanisms for deleting roles on PyPI was
  discovered by a security researcher, which would allow an attacker
  to remove roles for projects not under their control.
• Vulnerability in GitHub Actions workflow for
  PyPI^[6] – An exploitable
  vulnerability in a GitHub Actions workflow for PyPI’s source
  repository could allow an attacker to obtain write permissions
  against the pypa/warehouse repository.

Successful exploitation of the flaws could result in the
arbitrary deletion of project documentation files, which has to do
with how the API endpoint for removing legacy documentation handles
project names passed as input, and enable any user to delete any
role given a valid role ID due to a missing check that matches the
current project with the project the role is associated with.

A more critical flaw concerns an issue in the GitHub Actions
workflow for PyPI’s source repository named “combine-prs.yml,”
resulting in a scenario wherein an adversary could obtain write
permission for the main branch of the “pypa/warehouse” repository,
and in the process execute malicious code on pypi.org.

“The vulnerabilities described in this article had a significant
impact on the Python ecosystem,” RyotaK noted. “As I’ve mentioned
several times before, some supply chains have critical
vulnerabilities. However, a limited number of people are
researching supply chain attacks, and most supply chains are not
properly protected. Therefore, I believe that it’s necessary for
users who depend on the supply chain to actively contribute to
improving security in the supply chain.”