> External Variable Modification Vulnerability occurs when a web application improperly handles user input, allowing attackers to overwrite internal variables. In PHP, functions like extract($_GET), extract($_POST), or import_request_variables() can be abused if they import user-controlled data into the global scope without proper validation. This can lead to security issues such as unauthorized changes to application logic, privilege escalation, or bypassing security controls.
Source: External Variable Modification/README.md in PayloadsAllTheThings. From PayloadsAllTheThings by Swissky and contributors. MIT License, Copyright (c) 2019 Swissky.