Skip to main content

Lack of data validation - Header x-amzn-RequestId

Need​

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

Context​

  • Usage of Dart for building cross-platform applications
  • Usage of Shelf for managing data storage and retrieval

Description​

Non compliant code​

import 'package:shelf/shelf.dart' as shelf;

shelf.Response handleRequest(shelf.Request request) {
  var requestId = request.headers['x-amzn-RequestId'];
  
  // Process the request with the requestId
  // ...

  return shelf.Response.ok('Request processed.');
}

The above Dart code is an example of a server-side application using the Shelf framework. This code is vulnerable as it does not validate or sanitize the 'x-amzn-RequestId' header field from the incoming request.

In the handleRequest function, the 'x-amzn-RequestId' header is directly accessed from the request headers without any validation or sanitization:

var requestId = request.headers['x-amzn-RequestId'];

This is a security vulnerability as it allows an attacker to potentially inject malicious code or data into the 'x-amzn-RequestId' header field. If this data is used in a way that can cause harm (e.g., used in a database query, used as part of a command that gets executed, etc.), it can lead to serious security issues such as SQL injection, command injection, or data corruption.

To fix this vulnerability, the application should validate and sanitize all input data, including header fields, before using them. This can be done using regular expressions, white-listing, or other input validation techniques.

Steps​

  • Validate the 'x-amzn-RequestId' header before using it. This can be done by checking if the header exists and if it meets certain criteria (e.g., length, format).
  • Sanitize the 'x-amzn-RequestId' header to remove any potentially harmful characters. This can be done using a whitelist of allowed characters or a blacklist of disallowed characters.
  • Implement error handling to deal with invalid 'x-amzn-RequestId' headers. This could involve returning an error response or ignoring the header.
  • Consider using a library or framework that provides built-in protection against header injection attacks. This can help to ensure that your application is secure against this type of vulnerability.

Compliant code​

import 'package:shelf/shelf.dart' as shelf;

shelf.Response handleRequest(shelf.Request request) {
  var requestId = request.headers['x-amzn-RequestId'];

  // Validate the 'x-amzn-RequestId' header
  if (requestId == null || !isValidRequestId(requestId)) {
    return shelf.Response(400, body: 'Invalid x-amzn-RequestId header.');
  }

  // Sanitize the 'x-amzn-RequestId' header
  requestId = sanitizeRequestId(requestId);

  // Process the request with the requestId
  // ...

  return shelf.Response.ok('Request processed.');
}

bool isValidRequestId(String requestId) {
  // Check if the requestId meets certain criteria (e.g., length, format)
  // This is just a placeholder. Replace with your actual validation logic.
  return requestId.length <= 100;
}

String sanitizeRequestId(String requestId) {
  // Remove any potentially harmful characters
  // This is just a placeholder. Replace with your actual sanitization logic.
  return requestId.replaceAll(RegExp(r'[^a-zA-Z0-9\\-]'), '');
}

The updated code includes validation and sanitization of the 'x-amzn-RequestId' header.

Firstly, the isValidRequestId function is used to validate the 'x-amzn-RequestId' header. This function checks if the header exists and if it meets certain criteria (e.g., length, format). If the header is invalid, the function returns a 400 response with an error message.

Secondly, the sanitizeRequestId function is used to sanitize the 'x-amzn-RequestId' header. This function removes any potentially harmful characters from the header. This is done using a regular expression that matches any character that is not a letter, a number, or a hyphen.

Finally, the sanitized 'x-amzn-RequestId' header is used to process the request.

This approach helps to prevent header injection attacks by ensuring that only valid and safe 'x-amzn-RequestId' headers are used by the application.

References​

Last updated on