Exploiting dynamic rendering engines to take control of web apps

Dynamic rendering is a technique used to enhance the SEO capabilities of websites built with modern JavaScript frameworks like React, Angular, and Vue, which often struggle with search engine indexing due to their client-side rendering. This approach involves using headless browsers to generate HTML content server-side, which is then served to crawlers for indexing. Popular tools for dynamic rendering include Rendertron and Prerender, although they can introduce security vulnerabilities such as server-side request forgery (SSRF) if not configured correctly. The text details how these vulnerabilities can be exploited, as demonstrated by the author, who managed to exploit a vulnerability in Rendertron to gain unauthorized access to a production server, earning a $5,000 bug bounty. The risks associated with dynamic rendering include potential exposure of sensitive data and exploitability of cloud infrastructure, necessitating careful configuration and security practices. The author also emphasizes the importance of using tools like Semgrep for static analysis to identify vulnerabilities in applications using dynamic rendering.