What layer of the OSI model do web application firewalls like ModSecurity focus on when defending against attacks?

Web application firewalls, such as ModSecurity, operate primarily at the Application layer of the OSI model. This layer is responsible for handling high-level protocols and ensuring that application-level data is processed and secured effectively. By focusing on the Application layer, web application firewalls can analyze the traffic specific to web applications, including HTTP and HTTPS requests.

At this level, these firewalls can protect against various types of attacks that target web applications, such as SQL injection, cross-site scripting (XSS), and other vulnerabilities that exploit application logic. By inspecting the content of the requests and responses within the Application layer, ModSecurity can apply rules and filters to block malicious input and mitigate threats before they reach the underlying web application.

This specificity is crucial, as attacks often bypass defenses that focus on lower layers of the OSI model, which may not inspect the application-specific data that is critical for identifying threats. Therefore, the Application layer is where these firewalls provide their primary protective capabilities, making this answer the most accurate in the context of how web application firewalls function.