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Lack of data validation - Header x-amzn-RequestId

Need​

Implementation of robust data validation for the x-amzn-RequestId Header

Context​

  • Usage of TypeScript for adding static typing to JavaScript
  • Usage of Express for building web applications and APIs

Description​

Non compliant code​

import express from 'express';

const app = express();

app.use(express.json());

app.get('/api/data', (req, res) => {
  const requestId = req.headers['x-amzn-RequestId'];

  // Lack of data validation on the server side
  // Potentially dangerous character strings can be entered in the x-amzn-RequestId Header
  // This can lead to injection attacks or denial of service by using very long character strings
  // No server-side permission control is implemented to prevent modification of the requestId field

  // Process the request and return the response
  res.status(200).json({ requestId, data: 'Some data' });
});

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

The vulnerability in the provided TypeScript code is a lack of data validation on the server side for the "x-amzn-RequestId" header.

In the code, the application receives the value of the "x-amzn-RequestId" header from the incoming request using req.headers['x-amzn-RequestId']. However, there is no validation or sanitization of this value, allowing potentially dangerous character strings to be entered.

This vulnerability can have two potential impacts:

  1. Injection Attacks: An attacker can exploit this vulnerability by injecting dangerous character strings into the "x-amzn-RequestId" header. This could lead to various types of injection attacks, such as SQL injection, command injection, or cross-site scripting (XSS) attacks.

  2. Denial of Service: The lack of validation also allows an attacker to use very long character strings as the value of the "x-amzn-RequestId" header. This can potentially cause a denial of service (DoS) attack by overwhelming the server's resources and making it unresponsive.

To mitigate this vulnerability, it is recommended to implement server-side data validation for the "x-amzn-RequestId" header. This validation should ensure that only expected and safe characters are allowed in the header value. Additionally, server-side permission controls should be implemented to prevent unauthorized modification of the "requestId" field.

Steps​

  • Implement server-side data validation for the x-amzn-RequestId header
  • Define a set of allowed characters for the requestId field and validate incoming values against it
  • Consider limiting the length of the requestId field to prevent denial of service attacks
  • Implement server-side permission control to prevent unauthorized modification of the requestId field

Compliant code​

import express from 'express';

const app = express();

app.use(express.json());

app.get('/api/data', (req, res) => {
  const requestId = req.headers['x-amzn-RequestId'];

  // Server-side data validation for the x-amzn-RequestId header
  const allowedCharacters = /^[a-zA-Z0-9-_]+$/; // Define a set of allowed characters
  const maxLength = 50; // Limit the length of the requestId field

  if (!requestId || !allowedCharacters.test(requestId) || requestId.length > maxLength) {
    return res.status(400).json({ error: 'Invalid requestId' });
  }

  // Server-side permission control to prevent unauthorized modification of the requestId field
  // Implement your permission control logic here

  // Process the request and return the response
  res.status(200).json({ requestId, data: 'Some data' });
});

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

The fixed code addresses the vulnerability by implementing server-side data validation for the x-amzn-RequestId header. Here's an explanation of the changes made:

  1. The code uses the Express framework to create an HTTP server.
  2. The express.json() middleware is used to parse incoming JSON payloads.
  3. The /api/data route is defined to handle GET requests.
  4. Inside the route handler, the x-amzn-RequestId header value is extracted from the request headers.
  5. The code defines a regular expression allowedCharacters that represents the set of allowed characters for the requestId field. It allows alphanumeric characters, hyphen, and underscore.
  6. The maxLength variable is set to limit the length of the requestId field to 50 characters.
  7. The code checks if the requestId is missing, contains any disallowed characters, or exceeds the maximum length. If any of these conditions are true, a 400 Bad Request response is sent with an error message.
  8. The code then proceeds to implement server-side permission control logic to prevent unauthorized modification of the requestId field. This part is not shown in the code snippet and should be implemented separately based on the specific requirements of the application.
  9. Finally, if the requestId passes the validation and permission control, the code processes the request and returns a 200 OK response with the requestId and some sample data.

By implementing server-side data validation and permission control, the fixed code ensures that potentially dangerous character strings are not accepted in the x-amzn-RequestId header and prevents unauthorized modification of the field.

References​

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