LOTP

flake8

cli config-file eval-py

References

• https://flake8.pycqa.org/en/latest/user/configuration.html

flake8 is a popular Python linter, a tool to check Python code against coding standards.

Configuration Files .flake8, setup.cfg, tox.ini

When running, flake8 automatically discovers and reads its configuration from one of three files if present in the project root: .flake8, setup.cfg, or tox.ini.

These configuration files can instruct flake8 to load local plugins. A local plugin is a Python script located within the repository itself. This feature can be abused to achieve arbitrary python code execution.

An attacker can submit a pull request containing a malicious configuration file (e.g. .flake8) and a Python script. When a CI/CD workflow checks out the code and runs flake8, it will:

1. Read the malicious .flake8 file.
2. Load the local plugin specified in the file (pwn.py).
3. Execute the Python code within the plugin.

This provides a direct path to code execution on the runner. The same attack payload works for all three configuration file types.

# `.flake8` file

[flake8]
...

[flake8:local-plugins]
extension =
    malicious_plugin = script:main

In this example, the attacker defines a malicious main function in script.py that gets executes when flake8 ... is called.