Improper Neutralization of Equivalent Special Elements

This flaw often stems from an incomplete security filter. Developers might implement a defense against a specific list of characters, commands, or syntax patterns, but attackers can bypass these checks by using functionally equivalent alternatives. For example, a filter might block a single-dash command-line switch like `-e` but overlook the double-dash equivalent `--exec`, which performs the same operation. These bypasses frequently involve alternate encodings, different representations, or platform-specific expansions. On a Unix-like system, an application might filter out a leading slash (`/`) to prevent absolute file paths but not account for the tilde (`~username`) notation, which the shell expands to an absolute path. The core issue is that the validation logic does not understand the underlying semantics of the data it's processing, only its surface-level form.