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Message flooding

Need​

Prevention of message flooding and resource exhaustion

Context​

  • Usage of C# for building robust and scalable applications
  • Usage of _smsService for sending SMS messages
  • Usage of _emailService for sending emails
  • Usage of the Ok package for handling HTTP responses with a status code of 200

Description​

Non compliant code​

[HttpPost]
public async Task<IActionResult> SendMassMessages(List<string> phoneNumbers, List<string> emails, string message)
{
    foreach (var phoneNumber in phoneNumbers)
    {
        await _smsService.SendSmsAsync(phoneNumber, message);
    }

    foreach (var email in emails)
    {
        await _emailService.SendEmailAsync(email, message);
    }

    return Ok();
}

The above code is an example of an endpoint in an ASP.NET Core application that sends a mass message to a list of phone numbers and emails. This endpoint is vulnerable to message flooding attacks because it does not limit the number of messages that can be sent.

An attacker could exploit this vulnerability by sending a large number of requests to this endpoint with a long list of phone numbers and emails. This would result in a large number of messages being sent, which could saturate the inbox of the victims and consume their resources.

The _smsService.SendSmsAsync and _emailService.SendEmailAsync methods are used to send the messages. These methods could potentially consume a lot of resources if they are called a large number of times, which could lead to performance issues or even a denial of service.

Furthermore, there are no checks in place to verify that the phone numbers and emails provided in the request are valid or belong to the person making the request. This means that an attacker could potentially use this endpoint to send spam or malicious messages to arbitrary phone numbers or email addresses.

Steps​

  • Implement rate limiting to restrict the number of messages that can be sent within a certain time period.
  • Validate and sanitize the input data to prevent any malicious or excessive messages from being sent.
  • Implement a queue system to handle the sending of messages asynchronously, ensuring that resources are not consumed excessively.
  • Monitor and analyze the message sending process to detect any abnormal behavior or patterns that may indicate message flooding.
  • Implement user authentication and authorization to prevent unauthorized access to the message sending functionality.
  • Regularly update and patch the application and its dependencies to address any security vulnerabilities that may be exploited for message flooding.

Compliant code​

[HttpPost]
[Authorize]
[RateLimit(PerSecond = 5)]
public async Task<IActionResult> SendMassMessages(List<string> phoneNumbers, List<string> emails, string message)
{
    if (phoneNumbers.Count > 100 || emails.Count > 100)
    {
        return BadRequest("Too many messages");
    }

    foreach (var phoneNumber in phoneNumbers)
    {
        if (!IsValidPhoneNumber(phoneNumber))
        {
            return BadRequest("Invalid phone number");
        }

        await _messageQueue.Enqueue(() => _smsService.SendSmsAsync(phoneNumber, message));
    }

    foreach (var email in emails)
    {
        if (!IsValidEmail(email))
        {
            return BadRequest("Invalid email");
        }

        await _messageQueue.Enqueue(() => _emailService.SendEmailAsync(email, message));
    }

    return Ok();
}

private bool IsValidPhoneNumber(string phoneNumber)
{
    // Implement phone number validation logic here
}

private bool IsValidEmail(string email)
{
    // Implement email validation logic here
}

The updated code includes several measures to prevent message flooding:

  • Rate Limiting: The RateLimit attribute is used to limit the number of messages that can be sent per second. This prevents a user from sending too many messages in a short period of time.

  • Input Validation: The IsValidPhoneNumber and IsValidEmail methods are used to validate the phone numbers and emails before they are sent. This prevents invalid or malicious data from being sent.

  • Queue System: The _messageQueue.Enqueue method is used to add the message sending tasks to a queue. This allows the tasks to be processed asynchronously, preventing the server from being overwhelmed by too many tasks at once.

  • User Authorization: The Authorize attribute is used to ensure that only authenticated users can send messages. This prevents unauthorized users from accessing the message sending functionality.

  • Message Limit: The code checks if the number of phone numbers or emails exceeds 100. If it does, a "Too many messages" error is returned. This prevents a user from sending too many messages at once.

Regular updates and patches should also be applied to the application and its dependencies to address any security vulnerabilities that may be exploited for message flooding.

References​

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