Book Image

ASP.NET Core 5 Secure Coding Cookbook

By : Roman Canlas
Book Image

ASP.NET Core 5 Secure Coding Cookbook

By: Roman Canlas

Overview of this book

ASP.NET Core developers are often presented with security test results showing the vulnerabilities found in their web apps. While the report may provide some high-level fix suggestions, it does not specify the exact steps that you need to take to resolve or fix weaknesses discovered by these tests. In ASP.NET Secure Coding Cookbook, you’ll start by learning the fundamental concepts of secure coding and then gradually progress to identifying common web app vulnerabilities in code. As you progress, you’ll cover recipes for fixing security misconfigurations in ASP.NET Core web apps. The book further demonstrates how you can resolve different types of Cross-Site Scripting. A dedicated section also takes you through fixing miscellaneous vulnerabilities that are no longer in the OWASP Top 10 list. This book features a recipe-style format, with each recipe containing sample unsecure code that presents the problem and corresponding solutions to eliminate the security bug. You’ll be able to follow along with each step of the exercise and use the accompanying sample ASP.NET Core solution to practice writing secure code. By the end of this book, you’ll be able to identify unsecure code causing different security flaws in ASP.NET Core web apps and you’ll have gained hands-on experience in removing vulnerabilities and security defects from your code.
Table of Contents (15 chapters)

Fixing XXE injection with XmlDocument

The XmlDocument class has been the de facto XML parser for .NET applications. This XML parser object is often used to load, modify, and delete XML in-memory. It has an XmlResolver property, which enables the use of external XML resources such as DTDs.

Document Type Definition, most commonly known as DTD, is similar to XML files but holds information about an XML's composition or structure. It can have an ENTITY element, which can be internal or external. When an XDocument parses an XML file with a DTD, this XML parser will process it, along with its ENTITY declarations.

Let's look at some content of an XML file with malicious injected ENTITY declarations. This is a known classic example of the Billion Laughs attack, which is a Denial-of-Service (DoS) attack that targets XML parsers such as XmlDocument. Loading this XML will cause your ASP.NET Core web app to crash or become unresponsive:

<?xml version="1.0"?>...