Identifying Application Vulnerabilities

C.

To find out whether the application running on App Engine is using insecure binaries or is vulnerable to XSS attacks, the recommended service to use is the Cloud Security Scanner (Option C).

The Cloud Security Scanner is a web application security scanning tool that enables you to scan your App Engine, Compute Engine, and Google Kubernetes Engine applications for security vulnerabilities. It is an automated tool that crawls through your application's URLs and checks for common security vulnerabilities such as cross-site scripting (XSS), mixed content (HTTP/HTTPS), and outdated/insecure libraries.

Option A, Cloud Armor, is a security service that provides distributed denial of service (DDoS) protection and defends against web-based attacks. It is not designed specifically for finding insecure binaries or XSS attacks.

Option B, Stackdriver Debugger, is a tool for debugging production applications in real-time, but it is not designed for security testing.

Option D, Stackdriver Error Reporting, is a tool for monitoring and reporting errors in your application. While it can help identify potential security issues, it is not specifically designed for finding insecure binaries or XSS attacks.

Therefore, the correct answer is option C, Cloud Security Scanner, which is specifically designed for finding security vulnerabilities, including insecure binaries and XSS attacks, in your application.