## 2026-03-20 - Safe Path Traversal Prevention in Low-Level Utilities
**Vulnerability:** The generic file utility `hash_file` in `app/utils/file_operations.py` accepted any file path and was vulnerable to reading arbitrary files via path traversal (e.g., `../../../etc/passwd`) or absolute paths if an attacker could control the `filepath` argument.
**Learning:** Naively checking for `".." in path` breaks legitimate relative paths used internally by the application. Blocking absolute paths entirely also breaks functionality. Input validation should occur at the API boundary, but for defense-in-depth, low-level utilities must enforce expected boundaries (e.g., the application's `workdir`).
**Prevention:** Use `pathlib.Path.resolve()` on both the target path and the allowed base directory (`settings.workdir`). Ensure the resolved target path is strictly within the allowed boundary using `filepath_obj.relative_to(workdir_obj)`, catching the `ValueError` that is raised when the path is out of bounds. This safely blocks both relative traversal attacks and arbitrary absolute paths.