What are the potential security risks of allowing users to resubmit data in PHP applications?

Allowing users to resubmit data in PHP applications can lead to potential security risks such as duplicate submissions, data corruption, and potential vulnerabilities like CSRF attacks. To prevent these risks, it is important to implement proper validation and checks to ensure that data is only submitted once and that the application is protected against malicious actions. 

```php
// Check if the form has already been submitted
if ($_SERVER['REQUEST_METHOD'] == 'POST' && !empty($_POST['submitted'])) {
    // Process the form data
    // Add code here to handle form submission
    // Redirect to a different page after processing to prevent resubmission
    header("Location: success.php");
    exit;
}
```
In the above code snippet, we check if the form has already been submitted by checking the request method and the presence of a specific form field (in this case, 'submitted'). If the form has already been submitted, the code processes the form data and then redirects the user to a different page to prevent resubmission.

Keywords

SQL injection Cross-site scripting (XSS) CSRF attacks Form validation Session hijacking

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