How can you prevent cross-site scripting (XSS) attacks with design patterns?

2 Encode output data

Another way to prevent XSS is to encode output data before sending it to the browser. Encoding means converting special characters, such as <, >, or &, into their corresponding HTML entities, such as &lt;, &gt;, or &amp;. This way, the browser will not interpret them as HTML tags or scripts, but as plain text. You can use a design pattern called the encoder pattern to implement encoding logic in your web application. The encoder pattern defines an interface for encoding data and provides different implementations for different types of data, such as HTML, XML, or JSON. You can use the encoder pattern to encode any output data that originates from user input or external sources.

3 Use content security policy

A third way to prevent XSS is to use content security policy (CSP), which is a web standard that allows you to control what sources of content can be loaded and executed on your web pages. CSP can help you prevent XSS by restricting the sources of scripts, styles, images, or other resources that your web pages can use. You can use a design pattern called the policy pattern to implement CSP in your web application. The policy pattern defines an interface for applying policies and provides different implementations for different types of policies, such as CSP, CORS, or HSTS. You can use the policy pattern to define and enforce a CSP that only allows trusted sources of content on your web pages.

4 Use template engines

A fourth way to prevent XSS is to use template engines, which are tools that allow you to generate dynamic HTML content from data and templates. Template engines can help you prevent XSS by automatically escaping or encoding any data that is inserted into the HTML templates. You can use a design pattern called the template method pattern to implement template engines in your web application. The template method pattern defines an abstract class that specifies the steps for generating HTML content and provides concrete subclasses that implement the details of each step. You can use the template method pattern to create template engines that handle different types of data and templates.

5 Use proxy objects

A fifth way to prevent XSS is to use proxy objects, which are objects that act as intermediaries between your web application and the browser. Proxy objects can help you prevent XSS by intercepting and modifying any requests or responses that may contain malicious code. You can use a design pattern called the proxy pattern to implement proxy objects in your web application. The proxy pattern defines an interface for accessing an object and provides a proxy object that implements the same interface and delegates the requests to the original object. You can use the proxy pattern to create proxy objects that filter, validate, encode, or log any requests or responses that pass through them.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?