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Lack of data validation - Session Cookie


Implementation of secure data validation for Session Cookies


  • Usage of Dart for building cross-platform mobile, web, and desktop applications
  • Usage of Shelf for managing and organizing data in a Node.js application


Non compliant code

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

shelf.Response handleRequest(shelf.Request request) {
var sessionCookie = request.headers['cookie'];
var response = shelf.Response.ok('Session Created');
return response.change(headers: {'set-cookie': sessionCookie});

The above code represents a vulnerable implementation of session cookie handling in a Dart backend application using the Shelf framework.

The handleRequest function is designed to handle incoming HTTP requests. It retrieves the session cookie from the incoming request headers without any form of validation.

var sessionCookie = request.headers['cookie'];

This session cookie is then directly used to set the 'set-cookie' header in the response:

return response.change(headers: {'set-cookie': sessionCookie});

The vulnerability here lies in the lack of data validation. Any value sent from the client-side as a cookie is accepted and used to set the session cookie. This means an attacker could potentially send a malicious value as a cookie, which would then be set as the session cookie. This could lead to various security issues, including session hijacking or cross-site scripting (XSS) attacks, depending on how the session cookie is used throughout the application.

The code should be revised to include proper validation of the incoming session cookie to ensure its legitimacy and security.


  • Implement a server-side session management system that generates secure session cookies.
  • Do not trust any value sent from the client side. Always validate and sanitize the data.
  • Use a secure method to generate session cookies, such as a cryptographically secure pseudorandom number generator.
  • Set the HttpOnly attribute for the session cookie to prevent access from client-side scripts.
  • Set the Secure attribute for the session cookie to ensure it is only sent over HTTPS.
  • Consider using a framework or library that provides secure session management features.

Compliant code

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

String generateSessionId() {
var random =;
var values = List<int>.generate(16, (i) => random.nextInt(256));
return values.join();

shelf.Response handleRequest(shelf.Request request) {
var sessionId = generateSessionId();
var response = shelf.Response.ok('Session Created');
return response.change(headers: {
'set-cookie': 'sessionId=$sessionId; HttpOnly; Secure'

The updated code now includes a function generateSessionId() that generates a secure session ID using Dart's function, which provides a cryptographically secure random number. This session ID is then used to set the session cookie in the handleRequest() function.

The handleRequest() function no longer trusts the session cookie sent from the client. Instead, it generates a new, secure session ID every time it is called. This session ID is then used to set the sessionId cookie.

The set-cookie header has been updated to include the HttpOnly and Secure attributes. The HttpOnly attribute prevents the cookie from being accessed by client-side scripts, reducing the risk of cross-site scripting (XSS) attacks. The Secure attribute ensures that the cookie is only sent over HTTPS, preventing it from being intercepted and read by a third party.

This approach ensures that the session cookie is generated securely and cannot be tampered with by the client. It also ensures that the cookie is transmitted securely, reducing the risk of it being intercepted.