Why Use `exit()` After `header('Location...')` in PHP Redirection?

Redirection with header() in PHP: Understanding the Need for Exit()

In PHP, the header() function is used for redirection, sending instructions to the browser to navigate to a new URL. However, it's essential to invoke exit after header('Location..') to prevent subsequent PHP code execution.

Why the Need for Exit()?

By default, after sending a header, PHP continues to execute any remaining code. However, this can cause unexpected behavior when script execution proceeds beyond the redirect.

Consequences of Code Execution After Redirection

1. Data Exposure: Sensitive information or session data could be accessible even after redirection, defeating the purpose of the redirect.
2. Incorrect Behavior: The redirect may be overridden by subsequent code, resulting in unintended behavior.

Exploitation by Malicious Users

Malicious users can bypass the redirection by disabling redirect handling in their web browsers. Tools like wget allow users to retrieve the entire page, including data after the redirection, without being redirected.

Example of Code Execution After Redirection:

<?php
header('Location: new_page.php');
echo 'This code will be executed after the redirect.';
?>

In this example, the code 'This code will be executed after the redirect.' will be displayed even after the user is redirected to new_page.php.

Preventing Code Execution After Redirection

To prevent code execution after redirection, it's essential to invoke exit immediately following header('Location..'). This ensures that no further code is executed and the redirection takes full effect.

In conclusion, calling exit after header('Location..') is a critical security measure in PHP to prevent data exposure, ensure correct redirection behavior, and mitigate exploitation attempts by malicious users.

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