How it was found

The following Python library has been installed on at least one Yelp owned build server directly from the public PyPI registry.

• https://pypi.org/project/yelp-cgeom/

This package should normally be downloaded from the internal Yelp registry, but a misconfiguration appears to have caused it to be downloaded from pypi.org instead.

This package name was previously unclaimed on PyPI. In order to detect such misconfigurations, I have uploaded my own code under the yelp-cgeom name.

Whenever yelp-cgeom is installed, my setup.py script is executed on the machine where it is downloaded. The script sends a callback to my server containing:

• the originating IP
• the machine's hostname
• the current working directory

To avoid breaching the program policy, no further actions are taken.

Vulnerable machine

At Wed jul 29 2020 04:27:23 GMT, and again 20 seconds later, I have received the following callback:

• originating IP: 54.71.19.248
• hostname: 10-81-21-60-uswest2bdevc.uswest2-devc.yelpcorp.com
• home directory: /nail/home/jenkins
• directory: /ephemeral/tmpdir/pip-install-o6jnSv/yelp-cgeom

This indicates that my preinstall script was executed on the server above.

Impact

If this package had been claimed by an attacker, this would have led to arbitrary code execution on the affected server, as well as allowing the attacker to add backdoors inside the affected project(s) during the build process.