The article by Daoud Youssef provides a practical guide for testing Next.js applications, focusing on common vulnerabilities like SSRF, XSS, CSTI, SSTI, CSRF, and data leaks. Next.js, a full-stack framework for React, is gaining traction, currently powering around 2.3% of all websites, translating to over 20 million. Its popularity stems from its capabilities in server-side rendering (SSR) and static site generation (SSG), allowing developers to build both frontend and backend components seamlessly. Youssef details the attack surfaces testers should focus on during a black-box penetration test. For instance, while Next.js doesn't inherently support server-side template injection (SSTI) due to its use of JSX instead of traditional templating engines, developers can inadvertently introduce vulnerabilities when using libraries like EJS or Handlebars. Testing for SSTI involves injecting payloads into user inputs to see if they are executed or reflected back. Similarly, client-side template injection (CSTI) and cross-site scripting (XSS) risks arise mainly from unsafe coding practices, such as using `dangerouslySetInnerHTML`. This function can lead to vulnerabilities if developers improperly sanitize user inputs. The article emphasizes the importance of manual testing and understanding the framework's behavior. It suggests using tools like Burp Suite to identify risky patterns or functions in the codebase. Identifying any instances of `dangerouslySetInnerHTML` or client-side template engines can help testers pinpoint potential vulnerabilities. The focus is on being thorough and cautious, as even small oversights can lead to significant security issues in Next.js applications.