Upload endpoint CSRF vulnerability

Summary

A Cross Site Request Forgery vulnerability was discovered in the endpoint which accepts uploads to PyPI.

  • Disclosure date: 2020-02-22 (Reported via security policy on pypi.org)
  • Disclosed by: Joachim Jablon

Reported vulnerability

Upload endpoint vulnerable to CSRF

Although PyPI implements CSRF protection for endpoints with side effects throughout the views and endpoints for the primary web user interface, that protection is not implemented for the upload endpoint at https://upload.pypi.org/legacy/. This endpoint is not intended for browsers, but rather clients such as setuptools and twine which do not authenticate using HTTP Sessions or Cookies.

The upload endpoint was misconfigured to accept HTTP Session authentication cookies from pypi.org. Combined with intentional disabling of CSRF protection on this endpoint, an attacker could have constructed a form to trick PyPI users into uploading releases to PyPI.

Initially resolved in: https://github.com/pypa/warehouse/pull/7432

Assessment

We are unable to directly determine if this vulnerabilities was exploited. PyPI stores an Audit Log of events modifying user accounts and projects on the service. These log successful logins via the login form but were not configured to log authentication via other methods as they were assumed to be associated with package uploads only, which are logged separately.

Reccomendations

Users are encouraged to review their Account Security History regularly to determine if any suspicious activity has taken place. If you identify any such activity, please report it per our published security policy.

Timeline

  • 2020-02-22 Issue reported by Joachim Jablon to security@python.org per PyPI security policy on pypi.org
  • 2020-02-23 (+1days): Report investigated by Ernest W. Durbin III and determined to be valid.
  • 2020-02-24 (+2days): Fixes reviewd by PyPI administrators, deployed, and verified.