PEP 829 Makes Python Startup Safer, But Risk Remains

This report reviews Python PEP 829, which replaces dangerous .pth files with .start files to limit arbitrary exec at interpreter startup, and demonstrates that while the new format improves auditability it does not eliminate startup code execution. The author provides proofs-of-concept showing how .pth/.start entrypoint handling can be manipulated (including clearing shared entrypoint state to force .pth exec), explains attack implications for supply-chain persistence and startup abuse, and recommends mitigations such as using python -S, auditing site-packages, and using sys.addaudithook.