In the web services stack, which layer is vulnerable to fault code leaks?

• A. Discovery Layer
• B. Security Layer
• C. Access Layer
• D. Presentation Layer

Answer: (A)

Fault information leaks happen when error details are exposed in metadata that clients use to discover services. In the web services stack, the Discovery Layer is responsible for providing information about available services, endpoints, and how to interact with them. If this layer returns verbose fault codes, internal exception details, or specific error messages in its responses, an attacker can learn how the system is structured and which components might be vulnerable. That exposed metadata makes it easier to plan further attacks.

The other layers focus more on limiting access, securing communications, and presenting information to users, so they are less typically a source of fault code leakage. The Security Layer should sanitize errors and protect credentials, the Access Layer deals with who can call what, and the Presentation Layer should also avoid revealing sensitive details in the user interface. But the primary risk of fault code leakage in a web services stack is associated with the service discovery mechanism.