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Lack of data validation - Source Code

Need​

Implementation of robust data validation in the source code

Context​

  • Usage of Node.js v14.0.0 for server-side JavaScript development
  • Usage of Express for building web applications and APIs

Description​

Non compliant code​

import express from 'express';

const app = express();
const port = 3000;

app.get('/search', (req, res) => {
  const searchTerm = req.query.term;

  // Vulnerable regular expression
  const regex = new RegExp(searchTerm);

  // Perform some operation with the regex
  // ...

  res.send('Search results');
});

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

The vulnerability in this code lies in the lack of data validation when constructing a regular expression. The code takes a search term from the query parameter and uses it to create a regular expression object using the RegExp constructor.

The problem is that the search term is directly passed into the RegExp constructor without any validation or sanitization. This means that if an attacker sends a specially crafted search term, it could contain characters or sequences that have special meaning in regular expressions. These special characters could cause the regular expression evaluation to become extremely complex or even crash the server.

For example, if an attacker sends a search term like .*+?{}, which are special characters in regular expressions, the server may encounter unexpected behavior or crash when trying to evaluate the regular expression.

To mitigate this vulnerability, it is important to properly validate and sanitize user input before using it in regular expressions. This can be done by implementing input validation and sanitization techniques, such as using a whitelist of allowed characters or escaping special characters in the search term before constructing the regular expression.

Steps​

  • Validate the input data before using it in a regular expression
  • Implement a whitelist or blacklist approach to filter out potentially dangerous input
  • Use a safer regular expression pattern that does not allow for complex operations
  • Consider using a library or framework that provides built-in input validation and sanitization

Compliant code​

import express from 'express';

const app = express();
const port = 3000;

app.get('/search', (req, res) => {
  const searchTerm = req.query.term;

  // Validate the input data before using it in a regular expression
  const sanitizedTerm = searchTerm.replace(/[^\\w\\s]/gi, '');

  // Perform some operation with the sanitized term
  // ...

  res.send('Search results');
});

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

The fixed code addresses the vulnerability by implementing data validation before using the input in a regular expression.

First, the code imports the Express framework and creates an instance of the application. It sets the port number to 3000.

Then, it defines a route for the '/search' endpoint using the HTTP GET method. When a request is made to this endpoint, the code retrieves the search term from the query parameters of the request using req.query.term.

To address the vulnerability, the code applies data validation to the search term before using it in a regular expression. It uses the replace method with a regular expression /[^\\w\\s]/gi to remove any characters that are not alphanumeric or whitespace. This ensures that the search term only contains safe characters.

After validating the search term, the code can perform any necessary operations with the sanitized term. This part is not shown in the code snippet and should be implemented according to the specific requirements of the application.

Finally, the code sends a response with the message 'Search results' to the client.

The application listens for incoming requests on the specified port and logs a message to the console when the server is running.

Overall, the fixed code demonstrates the implementation of data validation to mitigate the vulnerability and ensure that only safe input is used in regular expressions.

References​

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