What are the potential security risks associated with using global variables in PHP functions?

Using global variables in PHP functions can pose security risks such as data leakage, unintended variable modification, and potential vulnerability to injection attacks. To mitigate these risks, it is recommended to avoid using global variables in functions and instead pass variables as parameters or use classes and objects to encapsulate data.

// Avoid using global variables in functions
function unsafeFunction() {
    global $userData;
    // Code that uses $userData
}

// Use parameters to pass variables instead
function safeFunction($userData) {
    // Code that uses $userData
}