The most secure method of handling dynamic file loading is to map user inputs to a strict whitelist. Instead of allowing users to pass filenames, pass a key or an index.

The result? The server reads and returns the password file.

It looks like you're referencing a classic Local File Inclusion (LFI) Path Traversal attack pattern.

The ultimate target in our example is /etc/passwd . On Unix‑like systems, this file stores user account information. Historically it contained hashed passwords; today those hashes are usually in /etc/shadow , but /etc/passwd still reveals usernames, user IDs, home directories, and default shells. An attacker armed with this list can:

Provide for secure file handling in your preferred language Explain how to configure a WAF to block these patterns

: This is a bypass technique for basic input filters. Many poorly programmed firewalls or sanitization scripts search for the standard relative directory sequence ../ (dot-dot-slash) and strip it out. By doubling the dots ( .... ), if the application strips ../ , the remaining characters often collapse back into a valid ../ sequence.