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Email flooding

Need​

Prevention of email flooding and inbox saturation

Context​

  • Usage of PHP 7.0 for server-side scripting and web development
  • Usage of Request for making HTTP requests
  • Usage of Mail for sending emails
  • Usage of SendMailable for sending email messages

Description​

Non compliant code​

public function sendEmail(Request $request) {
    $recipient = $request->input('email');
    $subject = $request->input('subject');
    $message = $request->input('message');

    for($i = 0; $i < 1000; $i++) {
        Mail::to($recipient)->send(new SendMailable($subject, $message));
    }

    return response()->json(['message' => 'Emails sent successfully']);
}

The above code is a function in a Laravel controller that sends an email to a recipient. The recipient's email address, the subject of the email, and the message body are all obtained from a POST request.

The vulnerability lies in the loop that sends the email. As you can see, the loop iterates 1000 times, meaning that it sends 1000 emails to the recipient. This can be used to flood the recipient's inbox and cause a denial of service as it may cause the email service to become unavailable due to the large number of emails being sent.

The code does not have any restrictions or checks in place to prevent this from happening. There is no rate limiting or check to see if too many emails are being sent to the same recipient in a short amount of time. This means that an attacker could potentially use this to flood an inbox with a large number of emails.

Steps​

  • Remove the loop that sends the email 1000 times. This is the main cause of the email flooding.
  • Implement a rate limiting mechanism to limit the number of emails that can be sent in a certain time period.
  • Add a CAPTCHA verification to the email sending process to prevent automated scripts from sending emails.
  • Implement a user authentication system to ensure that only authenticated users can send emails.
  • Consider using a queue system for sending emails to distribute the load over time.

Compliant code​

public function sendEmail(Request $request) {
    $recipient = $request->input('email');
    $subject = $request->input('subject');
    $message = $request->input('message');

    // Removed the loop that sends the email 1000 times
    Mail::to($recipient)->send(new SendMailable($subject, $message));

    return response()->json(['message' => 'Emails sent successfully']);
}

The original code had a loop that would send the same email 1000 times to the recipient. This was a major vulnerability as it could lead to email flooding, causing the recipient's inbox to be saturated.

The fixed code removes this loop, so only one email is sent per request. This prevents email flooding.

However, there are still other measures that should be taken to further secure the email sending process:

  • Implement a rate limiting mechanism: This would limit the number of emails that can be sent in a certain time period. Laravel provides a rate limiting middleware that can be used for this purpose.

  • Add a CAPTCHA verification: This would prevent automated scripts from sending emails. There are several CAPTCHA services that can be integrated into a Laravel application.

  • Implement a user authentication system: This would ensure that only authenticated users can send emails. Laravel provides a robust authentication system out of the box.

  • Use a queue system for sending emails: This would distribute the load over time, preventing the server from being overwhelmed by a large number of simultaneous email sending requests. Laravel provides a queue system that can be used for this purpose.

References​

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