register_argc_argv is a PHP configuration setting that controls whether the interpreter creates the $argc and $argv variables. In command-line use, these hold the argument count and argument list. In some web-server setups, enabling the setting can also make request input behave more like command-line arguments, which changes how PHP code sees and processes data.
This matters in cyber security because small PHP runtime differences can change exploitability. Code that assumes $argv is only used in CLI scripts may accidentally accept attacker-controlled values in a web request. That can help an attacker steer file paths, template logic, or unsafe command wrappers, especially in legacy applications. Defenders usually disable it unless a script truly needs argument variables, and they review code that reads request data as if it were trusted runtime input.