Web services are almost similar to web applications. It is possible that web services can be affected with all the common vulnerabilities that a normal web application can have. This has to be kept in mind when developing an API for a mobile app. Some common issues that we see in APIs are listed following:
Authentication/Authorization: When developing backend APIs it is very common to build custom authentication. It is possible to have vulnerabilities associated with authentication/authorization.
Session management: Session management in mobile platforms is typically done using an authentication token. When the user logs in for the first time, he will be given an authentication token, and this will be used for the rest of the session. If this authentication token is not properly secured till it's destroyed, it may lead to an attack. Killing the session at the client side but not at the server is another common problem that is seen in mobile apps.
Input validation:...