gabrielmoreira Input Validation and Sanitization
Validation principles:
- Validate at the system boundary (API layer, form handler) — not deep in business logic.
- Validate type, range, length, and format explicitly.
- Reject unexpected input by default (allowlist > denylist).
SQL injection prevention: Always use parameterized queries or an ORM.
XSS prevention: Escape HTML output; use Content-Security-Policy headers; avoid innerHTML with user data.
Path traversal prevention: Resolve paths to canonical form and verify they are under the expected directory.
import os
base = '/allowed/dir'
canonical = os.path.realpath(os.path.join(base, user_input))
assert canonical.startswith(base + os.sep)