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Security controls bypass or absence - Session Invalidation

Need​

Enhancement of security controls for session invalidation

Context​

  • Usage of Dart 2.0 for developing high-performance, 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 sessionCode = request.headers['session-code'];

  if (sessionCode == null) {
    return shelf.Response.forbidden('Missing session code.');
  }

  if (sessionCode.contains('auto')) {
    return shelf.Response.ok('Access granted.');
  } else {
    return shelf.Response.forbidden('Invalid session code.');
  }
}

The handleRequest function is supposed to check the validity of a session code provided in the headers of a request. If the session code is missing, it correctly responds with a 403 Forbidden status code.

However, there is a major security flaw in the code. If the session code contains the string 'auto', the function grants access regardless of whether the session code is valid or not. This is because the sessionCode.contains('auto') condition checks if the session code contains 'auto' and returns an OK response if it does.

This means that an attacker could bypass the session validation by simply including 'auto' in their session code. This is a clear case of security controls bypass, as the session validation is not functioning as intended.

The vulnerability likely arose due to leftover debug code. During the debugging phase, it's common to use shortcuts or bypasses to make testing easier. However, these shortcuts should always be removed before the code is deployed to production. In this case, the 'auto' bypass was not removed, leading to a significant security vulnerability.

Steps​

  • Remove the condition that checks if the session code contains the word 'auto'. This condition is a security risk as it allows anyone with a session code containing 'auto' to gain access.
  • Implement a proper session validation mechanism. This could involve checking the session code against a database of valid session codes, or using a secure method to generate and validate session codes.
  • Ensure that session codes are invalidated after a certain period of time or after they have been used. This prevents an attacker from reusing a session code.
  • Consider using a security framework or library that provides built-in mechanisms for session management. This can help to ensure that your session management code is secure and reliable.

Compliant code​

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

shelf.Response handleRequest(shelf.Request request) {
  var sessionCode = request.headers['session-code'];

  if (sessionCode == null) {
    return shelf.Response.forbidden('Missing session code.');
  }

  // Implement a proper session validation mechanism here
  // For example, check the session code against a database of valid session codes
  if (!isValidSessionCode(sessionCode)) {
    return shelf.Response.forbidden('Invalid session code.');
  }

  return shelf.Response.ok('Access granted.');
}

bool isValidSessionCode(String sessionCode) {
  // Implement your session code validation logic here
  // This is just a placeholder
  return sessionCode != 'auto';
}

The updated code removes the security vulnerability by eliminating the condition that checks if the session code contains the word 'auto'. Instead, it introduces a new function isValidSessionCode() that should contain the logic for validating session codes. This function is currently a placeholder and should be replaced with actual validation logic, such as checking the session code against a database of valid session codes.

The handleRequest() function now checks if the session code is null, and if it is, it returns a forbidden response. If the session code is not null, it checks if the session code is valid using the isValidSessionCode() function. If the session code is valid, it returns an OK response, otherwise it returns a forbidden response.

This code ensures that only valid session codes are accepted, and that session codes containing 'auto' are not automatically accepted. This greatly improves the security of the application by preventing unauthorized access.

References​

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