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Lack of data validation - Emails

Need​

Implementation of email address validation to prevent registration with disposable mailboxes

Context​

  • Usage of TypeScript for statically typed JavaScript development
  • Usage of Express for building web applications and APIs

Description​

Non compliant code​

import express from 'express';

const app = express();

app.post('/register', (req, res) => {
  const email = req.body.email;

  // Vulnerable code: Lack of data validation for disposable mailboxes
  // No check is performed to ensure that the email does not belong to a disposable mailbox

  // Register the user with the provided email
  // ...

  res.send('User registered successfully');
});

app.listen(3000, () => {
  console.log('Server started on port 3000');
});

The vulnerability in the provided code is the lack of data validation for disposable mailboxes when registering users. The code does not perform any check to ensure that the email provided by the user does not belong to a disposable mailbox service such as yopmail.

This vulnerability can lead to potential security issues. Disposable mailboxes are temporary email addresses that can be easily created and discarded. They are commonly used for spamming or for malicious activities. By not validating the email addresses and allowing users to register with disposable mailboxes, the application becomes susceptible to abuse.

An attacker can exploit this vulnerability by registering with a disposable mailbox email address. Once registered, they can then initiate a password reset process. Since disposable mailboxes are temporary and can be accessed by anyone, the attacker can easily intercept the password reset email and gain unauthorized access to the registered user's account.

To mitigate this vulnerability, it is recommended to implement a blacklisting system that checks the email domain against a list of known disposable mailbox domains. If the email belongs to a disposable mailbox, the registration process should be rejected. Alternatively, implementing federated authentication, such as using social media accounts or single sign-on services, can also help mitigate this vulnerability as these services typically have their own email validation mechanisms in place.

Steps​

  • Implement data validation for the email field to ensure it does not belong to a disposable mailbox domain
  • Create a list of disposable mailbox domains or use a third-party API to check if the email domain is disposable
  • Before registering the user, check if the email domain is in the list of disposable mailbox domains
  • If the email domain is disposable, reject the registration request or prompt the user to provide a different email
  • Implement proper error handling and response messages for the rejected registration requests

Compliant code​

import express from 'express';

const app = express();

// List of disposable mailbox domains
const disposableDomains = ['yopmail.com', 'example.com', 'disposablemail.com'];

app.post('/register', (req, res) => {
  const email = req.body.email;

  // Check if the email domain is in the list of disposable mailbox domains
  const domain = email.split('@')[1];
  if (disposableDomains.includes(domain)) {
    res.status(400).send('Disposable mailbox domains are not allowed');
    return;
  }

  // Register the user with the provided email
  // ...

  res.send('User registered successfully');
});

app.listen(3000, () => {
  console.log('Server started on port 3000');
});

The fixed code addresses the vulnerability by implementing data validation for email addresses.

First, the code imports the necessary modules, including the Express framework. Then, it creates an instance of the Express application.

The code defines an array called disposableDomains which contains a list of known disposable mailbox domains. These domains are commonly used for temporary or disposable email addresses.

The code sets up a route for the /register endpoint using the app.post method. This endpoint is responsible for handling user registration requests.

Inside the route handler, the code retrieves the email address from the request body. It then extracts the domain from the email address using the split method.

Next, the code checks if the extracted domain exists in the disposableDomains array using the includes method. If the domain is found in the array, it means that the email belongs to a disposable mailbox domain.

In that case, the code sends a response with a status code of 400 and a message indicating that disposable mailbox domains are not allowed. This prevents the registration of users with disposable email addresses.

If the email domain is not in the disposableDomains array, the code proceeds to register the user with the provided email address. The actual registration logic is not shown in the code snippet.

Finally, the code starts the server and listens on port 3000, logging a message to indicate that the server has started.

By implementing this data validation check, the code ensures that only valid email addresses, excluding disposable mailbox domains, are allowed for user registration.

References​

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