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Lack of data validation - Input Length

Need​

Implementation of input length validation

Context​

  • Usage of TypeScript for statically typed JavaScript development
  • Usage of Express for building web applications and handling HTTP requests

Description​

Non compliant code​

import express from 'express';

const app = express();
app.use(express.json());

app.post('/endpoint', (req, res) => {
  const { data } = req.body;
  // No data validation for input length

  // Process the data
  // ...

  res.status(200).json({ message: 'Data processed successfully' });
});

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

The vulnerability in this code is the lack of data validation for input length in the /endpoint route. The code receives a POST request and extracts the data property from the request body. However, there is no validation to check the length of the data input.

This lack of validation allows an attacker to send massive amounts of data in the request body, potentially overwhelming the server and causing denial of service (DoS) attacks. By not enforcing a character limit on the input, the server becomes vulnerable to resource exhaustion and performance degradation.

To mitigate this vulnerability, it is recommended to implement server-side validation to ensure that user entries comply with a character limit. This can be done by checking the length of the data input and rejecting requests that exceed the allowed limit.

Steps​

  • Add a validation function to check the length of the 'data' field in the request body
  • Set a maximum allowed length for the 'data' field
  • If the length of the 'data' field exceeds the maximum allowed length, return an error response
  • Update the code to use the validation function before processing the data

Compliant code​

import express from 'express';

const app = express();
app.use(express.json());

const MAX_DATA_LENGTH = 100; // Set maximum allowed length for 'data' field

function validateDataLength(req, res, next) {
  const { data } = req.body;
  if (data.length > MAX_DATA_LENGTH) {
    return res.status(400).json({ error: 'Data length exceeds the maximum allowed length' });
  }
  next();
}

app.post('/endpoint', validateDataLength, (req, res) => {
  const { data } = req.body;
  
  // Process the data
  // ...

  res.status(200).json({ message: 'Data processed successfully' });
});

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

The fixed code addresses the vulnerability by implementing data validation on the server side to ensure that user entries comply with a character limit.

First, the code imports the necessary dependencies, including the Express framework.

The code sets a constant variable MAX_DATA_LENGTH to define the maximum allowed length for the 'data' field.

Next, a middleware function validateDataLength is defined. This function is responsible for validating the length of the 'data' field in the request body. It retrieves the 'data' field from the request body and checks if its length exceeds the MAX_DATA_LENGTH. If the length exceeds the limit, it returns a 400 status code with an error message indicating that the data length exceeds the maximum allowed length. Otherwise, it calls the next() function to proceed to the next middleware or route handler.

The code then sets up a POST route for the '/endpoint' endpoint. The validateDataLength middleware is added as a middleware function before the route handler. This ensures that the data length is validated before further processing.

Inside the route handler, the 'data' field is retrieved from the request body and can be processed further as needed.

Finally, the server is started on port 3000, and a console log message is displayed to indicate that the server is running.

Overall, this fixed code ensures that the length of the 'data' field is validated on the server side, preventing the possibility of sending massive amounts of characters and expanding attack vectors.

References​

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