An ASP .NET application must enable custom error pages in order to prevent attackers from mining information from the framework's built-in responses.
Handle exceptions appropriately in source code. ASP .NET applications should be configured to use custom error pages instead of the framework default page.
Do not attempt to process an error or attempt to mask it.
Verify return values are correct and do not supply sensitive information about the system.
Default error pages gives detailed information about the error that occurred, and should not be used in production environments. Attackers can leverage the additional information provided by a default error page to mount attacks targeted on the framework, database, or other resources used by the application.