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  • npm lifecycle scriptsscripts field in package.jsonNode.js
  • setup.py arbitrary code executionsetup.py in source distributions (sdist)Python
  • NODE_OPTIONS preload injectionNODE_OPTIONS environment variable, CLI flags, or .env files loaded via --env-fileNode.js
  • .pth file import execution*.pth files on sys.path (commonly site-packages)Python
  • binding.gyp / node-gyp native compilationbinding.gyp file in the package rootNode.js
  • Corepack (packageManager field)"packageManager" field in package.json, COREPACK_HOME cache directoryNode.js
  • .npmrc registry manipulation.npmrc file (project, user, or global)Node.js
  • overrides / resolutions dependency swapoverrides (npm) or resolutions (Yarn) field in package.jsonNode.js
  • pnpm hooks (pnpmfile.cjs).pnpmfile.cjs in the project rootNode.js
  • .yarnrc.yml plugins and registry.yarnrc.yml in the project rootNode.js
  • pyproject.toml build backendspyproject.toml [build-system] tablePython
  • sitecustomize / usercustomize auto-importsitecustomize.py / usercustomize.py on sys.path (usually site-packages)Python
  • .node native addon loading.node files in node_modules/ (typically under build/Release/ or prebuilds/)Node.js
  • Yarn Plug'n'Play (.pnp.cjs).pnp.cjs in the project rootNode.js
  • __init__.py execution on import__init__.py in any package directory on sys.pathPython
  • .pyc bytecode cache poisoning.pyc files in __pycache__/ directories alongside source modulesPython
  • PYTHONPATH / PYTHONHOME module shadowingPYTHONPATH / PYTHONHOME environment variablesPython
  • npx / npm exec remote executionnpx, npm exec, npm create / npm init (initializer flows)Node.js
  • conftest.py auto-loading (pytest)conftest.py files in any directory pytest traversesPython
  • NODE_PATH environment variableNODE_PATH environment variableNode.js
  • "imports" field (subpath imports)imports field in package.jsonNode.js
  • require.extensions / Module._extensionsrequire.extensions / Module._extensions in any loaded moduleNode.js
  • .egg files and EGG-INFO scripts.egg files in site-packages (registered via easy-install.pth)Python
  • Zip imports (zipimport).zip / .pyz files on sys.path, or passed directly to the interpreterPython
  • PYTHONSTARTUP environment variablePYTHONSTARTUP environment variablePython
  • node_modules/.hooks/ directorynode_modules/.hooks/ directoryNode.js
Python
Module resolution/File on disk/Deprecated

.egg files and EGG-INFO scripts

On import once the egg is on sys.path; EGG-INFO scripts at install time

Lives in
.egg files in site-packages (registered via easy-install.pth)
Attacker needs
Supply-chain foothold, Filesystem write access
Lifecycle
Install
Startup
your code
Module load
Runtime
REPL

Runs on import or require, for every module the app loads.

How it runs

Eggs came before wheels. An egg is a zip archive that holds a Python package plus metadata. easy_install dropped them into site-packages and registered them on sys.path through easy-install.pth. The same zipimport machinery applies, so an egg can carry an __init__.py with arbitrary code, or modules that shadow standard-library names.

Eggs are deprecated in favor of wheels, but they haven't died out. Legacy codebases, old internal repos and pinned setuptools versions keep them around. The EGG-INFO directory can also hold scripts that easy_install executes during installation, which is a second way to run code at install time.

Defend

Migrate off eggs to wheels; pin modern setuptools; audit easy-install.pth and legacy internal package repos.