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Lack of data validation - Special Characters

Need​

Implementation of input validation for special characters

Context​

  • Requirement of Node.js v14.0.0 or later for running the application
  • Usage of Express for building web applications and APIs

Description​

Non compliant code​

import express from 'express';

const app = express();

app.post('/user', (req, res) => {
  const { username } = req.body;

  // Lack of data validation for special characters
  // Any special characters are allowed in the username field

  // Process the user data
  // ...

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

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

The vulnerability in this code is the lack of data validation for special characters in the username field. The code does not check whether the username contains any special characters, allowing any special characters to be entered.

This can lead to unexpected behavior of the application. For example, if the application uses the username field to generate URLs or perform database queries, special characters could potentially cause errors or security vulnerabilities. Special characters can also disrupt the application's functionality if they are not properly handled.

To mitigate this vulnerability, it is recommended to validate all fields, including the username field, to ensure that no special characters are entered. This can be done by implementing input validation or using regular expressions to check for the presence of special characters before processing the user data.

Steps​

  • Import a data validation library, such as 'validator', into your project.
  • Add a validation function to check if the username contains any special characters.
  • Use the validation function to validate the username before processing the user data.
  • If the username contains special characters, return an error response to the client.
  • If the username is valid, proceed with processing the user data.
  • Update the response message to indicate whether the user was created successfully or not.

Compliant code​

import express from 'express';
import validator from 'validator';

const app = express();

app.use(express.json());

app.post('/user', (req, res) => {
  const { username } = req.body;

  // Validate that no special characters are entered in the username field
  if (validator.isAlphanumeric(username)) {
    // Process the user data
    // ...

    res.send('User created successfully');
  } else {
    res.status(400).send('Invalid username. Special characters are not allowed.');
  }
});

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

The fixed code addresses the vulnerability by implementing data validation to ensure that no special characters are entered in the username field.

The code uses the Express framework and imports the necessary modules, including express and validator. It sets up an Express application and configures it to parse JSON data.

The vulnerable endpoint /user is modified to include data validation. When a POST request is made to this endpoint, the code extracts the username field from the request body.

To validate the username, the code uses the isAlphanumeric function from the validator module. This function checks if the input string contains only alphanumeric characters (letters and numbers). If the username passes the validation, the code proceeds to process the user data and sends a success response.

If the username contains special characters, the code sends a 400 Bad Request response with an error message stating that special characters are not allowed.

By implementing this validation, the code ensures that only valid usernames without special characters are accepted, mitigating the vulnerability.

References​

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