A vulnerability in setuptools on Windows allows an attacker to craft a wheel file with malicious content in the namespace_packages.txt metadata. This can cause setuptools' legacy wheel installation to create an __init__.py file outside the intended installation directory, at a filesystem path influenced by the attacker. The created file has fixed content and is created with the permissions of the installing process. The issue requires the target directory to already exist and affects setuptools versions before 2026.09.09_1.